The Vitality Blast returns on Wednesday, with the format reverting to two groups of nine rather than last summer's three groups of six. Fixtures are packed in to keep the competition into a relatively tight group-stage window, with the quarter-finals from August 24-27 and Finals Day on September 18. In a change to previous regulations, counties can register three overseas players simultaneously - though can still only field two in a playing XI.

So, who are the runners and riders in the South Group?

Essex

Last season: 5th in South Group
Coach: Anthony McGrath
Captain: Simon Harmer
Overseas players: Harmer, James Neesham

Championship contrast: The leading red-ball side in the country over the last few years, Essex have been inconsistent in T20 - perhaps in part because they rely on a similar group of players having to make the switch between formats. The likes of Alastair Cook and Nick Browne will make way, with Varun Chopra coming in to add power at the top of the order, probably alongside Tom Westley. Jimmy Neesham's all-round ability should help balance the side, while youngsters like Aron Nijjar and Ben Allison could get opportunities.

Key man: Ryan ten Doeschate will turn 41 at the end of the month but he continues to show that age is one of the least-significant numbers for the analysts to crunch. Having helped Essex to lift their maiden T20 title in 2019, he had his best campaign in several years last summer, finishing as Essex's top-scorer and with a strike rate above his career average. Championship form has been middling but the Blast might help free him up.

One to watch: The latest young Essex seamer to catch the eye is Jack Plom, a neat-and-tidy right-armer who claimed seven wickets in his five appearances last year, to go with an impressive economy of 7.74. The 21-year-old is a former England Under-19 and comes into the competition in wicket-taking form for Essex in the 2nd XI T20 competition.

Verdict: Squeeze into the quarter-finals and, like in 2019, who knows what might happen? Alan Gardner

Bet365: 12/1

Glamorgan

Last season: 5th in Central Group
Coach: Matt Maynard
Captain: Chris Cooke
Overseas players: Marnus Labuschagne, Colin Ingram, Michael Neser

Championship contrast: Colin Ingram is the key addition, while Prem Sisodiya's left-arm spin should be effective in the Powerplay again, but the core of players is largely the same. Marnus Labuschagne is expected to play ahead of Michael Neser in the second overseas spot.

Key man: Colin Ingram, Glamorgan's all-time leading run-scorer in T20 cricket, returns to Cardiff after missing last year's Blast. He was not at his best in the Big Bash and the PSL earlier this year and turns 36 towards the end of the group stage but is undoubtedly the key man in their batting line-up, not least with last year's leading run-scorer, Andy Balbirnie, not returning.

One to watch: Marnus Labuschagne's presence brings intrigue: he has played only 16 T20s in his career with a middling record, though was effective as an anchor and leggie in a handful of games for Brisbane Heat in early 2021. He is available throughout after logistical concerns denied him a spot in Australia's enlarged white-ball squad to tour the Caribbean and has openly targeted a place in the T20 World Cup squad later this year.

Verdict: Plenty of spin options but Cardiff tends to favour seamers, where they are lighter. Quarter-final hopes depend heavily on Ingram, Labuschagne and Chris Cooke's runs from the middle order. Matt Roller

Bet365: 33/1

Gloucestershire

Last season: 1st in Central Group, semi-finalists
Coach: Ian Harvey
Captain: Jack Taylor
Overseas players: Glenn Phillips, Graeme van Buuren, Daniel Worrall

Championship contrast: Jack Taylor and Benny Howell come into the side while Ian Cockbain, Tom Smith and George Scott are all better-suited to the shorter format and Daniel Worrall's new-ball swing bowling should be effective. After consecutive innings defeats in the Championship, a change in formats comes at the right time.

Key man: Gloucestershire were dominant last season before losing an 11-over shoot-out in the semi-finals, and Glenn Phillips could be the missing piece in the jigsaw. An ultra-attacking middle-order batter who has cemented his spot in New Zealand's T20I side, he has honed his game against spin across four seasons playing for Jamaica Tallawahs in the CPL, and is likely to keep wicket with James Bracey on England duty.

One to watch: Chris Dent had not played a T20 since 2016 and had a dreary record in the format heading into last summer, but teed off at the top of the order, striking at 153.30 and finishing second to Cockbain in Gloucestershire's run charts. Training using weighted bats with the power-hitting coach Julian Wood appears to have transformed his white-ball game.

Verdict: Dark horses no more, after reaching Finals Day for the first time since 2004 last summer. For a squad filled with canny and underestimated T20 operators, anything less than a second visit to Edgbaston in a row would be a failure. MR

Bet365: 16/1

Hampshire

Last season: 6th in South Group
Coach: Adi Birrell
Captain: James Vince
Overseas players: Kyle Abbott, Colin de Grandhomme, D'Arcy Short

Championship contrast: The core of the team is the same. James Vince is captain in both formats and forms part a strong spine alongside Sam Northeast, Liam Dawson, Lewis McManus and Kyle Abbott, with the likes of James Fuller and Chris Wood adding power and nous. D'Arcy Short was a success at the top of the order for Durham two seasons ago, Colin de Grandhomme can play the finisher's role and provide useful overs, and Mason Crane's legspin should be a trump card.

Key man: Vince is one of the leading T20 batsmen in the world - over the last two years, only Alex Hales has scored more runs than him in the major domestic leagues, during which time he has twice helped Sydney Sixers to the Big Bash title. A member of the Hampshire golden generation that won the tournament in 2010 and 2012, Vince's ability to set the tone could be key for the current side.

One to watch: Crane was the side's leading wicket-taker last season and seems forever on the fringes of international selection (when fit). Having spent the winter touring as a reserve with England, the Blast provides an ideal opportunity to press his credentials again after limited opportunities in the early stages of the Championship.

Verdict: Serial Finals Day attendees a decade ago, Hampshire only won two games last year. Improving shouldn't be hard but a return to the glory days seems less straightforward. AG

Bet365: 10/1

Kent

Last season: 3rd in South Group
Coach: Matt Walker
Captain: Sam Billings
Overseas players: Qais Ahmad, Adam Milne, Heino Kuhn

Championship contrast: Depleted four-day squad will be bolstered by return of Matt Milnes and Harry Podmore from injury, and Fred Klaassen from international duty. Alex Blake is on a white-ball contract, while Joe Denly and Daniel Bell-Drummond will relish a change in formats. Sam Billings' availability may be limited by England duty. Will there be room for Darren Stevens, whose last T20 game for Kent was in 2017?

Key man: Joe Denly missed two Championship games for personal reasons last month but made a fluent 63 in his return last week. He will likely anchor the innings with Daniel Bell-Drummond - who enjoyed a breakthrough T20 season last summer, with 423 runs at a strike rate of 154.94 - given licence to go hard, and in the absence of the retired Imran Qayyum, his legspin will be relied upon in the middle overs and possibly in the Powerplay too.

One to watch: Mohammad Amir's 11th-hour withdrawal means Adam Milne returns for a fourth Blast season as the spearhead of Kent's attack, and his record for the club - 38 wickets at 19.10, with an economy rate of 7.34 - is testament to his effectiveness in all three phases of an innings, bowling at speeds in excess of 90mph/145kph. His recent form has won him a T20I recall, but careful management will be required, given his injury history.

Verdict: Consistently quarter-final contenders and should challenge again despite Qayyum's retirement leaving a hole to fill. MR

Bet365: 12/1

Middlesex

Last season: 4th in South Group
Coach: Stuart Law
Captain: Eoin Morgan
Overseas players: Chris Green, Daryl Mitchell, Mujeeb Ur Rahman, Paul Stirling

Championship contrast: A break from four-day cricket is possibly just what Middlesex need, after six defeats in eight in the Championship. Eoin Morgan is available for the start of the competition and there will be a familiar face donning T20 pink again as Paul Stirling returns to his old county for the first five games as an overseas signing. Steven Finn, having played just two Championship fixtures, is likely to deputise as captain when Morgan is with England, and youngsters such as James Cracknell, Luke Hollman and Blake Cullen will come into contention.

Key man: Legspinners are high up the list of must-haves in T20, and Middlesex could field two in Hollman - who also offers with the bat - and Nathan Sowter. The latter is Middlesex's senior spinner in white-ball cricket, and his T20 record is solid; over the last two Blast seasons, Matt Parkinson and Simon Harmer are the only spinners to have had more success.

One to watch: Max Holden was dropped from the Championship XI after averaging 14.77 from 10 innings, but he seems set to be given a chance to rediscover his spark in the shortest form. Holden scored a maiden T20 hundred from 59 balls at Chelmsford last year and his opening partnership with Stevie Eskinazi could be key.

Verdict: A middle-of-the-pack side on paper but Morgan's presence and some decent overseas signings could lift them into contention. AG

Bet365: 12/1

Somerset

Last season: 4th in Central Group
Coach: Jason Kerr
Captain: Lewis Gregory
Overseas players: Devon Conway, Marchant de Lange

Championship contrast: Max Waller brings a wealth of experience with his flat legbreaks, but the core of the squad is the same.

Key man: Tom Banton was county cricket's breakthrough white-ball player in 2019 but has struggled over the last year and opened up about the stress of quarantine and long Covid to ESPNcricinfo last month. He should be freed up by the opportunity to target Taunton's short boundaries, and with Babar Azam not returning (Devon Conway arrives after the World Test Championship final) there is pressure on him to pile on the runs.

One to watch: Death bowling has been Somerset's Achilles heel ever since Alfonso Thomas' retirement so Marchant de Lange, their full-season overseas signing, has a big role to play. He is best used as a middle-overs enforcer, but has some pedigree bowling at the death for Glamorgan, and a career economy rate in the last four overs of 9.41 is serviceable.

Verdict: Conway's arrival should boost their quarter-final prospects. MR

Bet365: 9/1

Surrey

Last season: 1st in South Group, finalists
Coach: Vikram Solanki
Captain: Jade Dernbach
Overseas players: Hashim Amla

Championship contrast: Jason Roy, Sam and Tom Curran return from the IPL and will be available for the start of the competition, while Laurie Evans, Will Jacks, Dan Moriarty and Gareth Batty will play greater roles. Reece Topley, Liam Plunkett and Sean Abbott are all injured.

Key man: Laurie Evans is among England's best uncapped white-ball batters and was vital in Surrey's run to the final last year, averaging 45.37 and striking at 153.16. He was the second-highest run-scorer in the LPL over the winter, with a remarkable strike rate of 182.35 against spin while playing for Colombo Kings. At 33, he should be at his peak.

One to watch: Jamie Overton leaked more than 10 runs an over with the ball in his first Blast season for Surrey but was dubbed "our Andre Russell" by Gareth Batty after striking at 194.33 in his five innings as a finisher. Injury crisis among seamers may see him required to bowl more regularly again but his potential with the bat gives them two finishers in him and Jordan Clark.

Verdict: Bowling attack is reliant on triple spin threat of Jacks, Moriarty and Batty but the same formula helped them top the group last summer. Should stay in quarter-final race throughout group stage. MR

Bet365: 13/2

Sussex

Last season: 2nd in South Group
Coach: James Kirtley
Captain: Luke Wright
Overseas players: Travis Head, David Wiese, Rashid Khan

Championship contrast: Significant overhaul, with Luke Wright, David Wiese, Ravi Bopara, Chris Jordan, Will Beer and Tymal Mills added to the group and Phil Salt set to return from injury. James Kirtley, the assistant coach in the Championship, takes the reins from Ian Salisbury for the Blast.

Key man: David Wiese returns for his sixth Blast season as an overseas player rather than a Kolpak, and has been in the country for a month preparing. He was the picture of consistency last year in a volatile finishing role, averaging 40.14 while striking at 145.59, and forms part of an imposing engine room from Nos. 3-6 alongside Travis Head, Delray Rawlins and Ravi Bopara. Will play less of a role with the ball this year.

One to watch: George Garton was rested from the Championship side last week to prepare for the Blast and warmed up with 30 not out off seven balls in a 2nd XI fixture. He had a breakthrough T20 season in 2020, taking 14 wickets spread across the Powerplay and the death overs, and won a game against Middlesex almost single-handedly from No. 8. Sussex also rate him as the club's best fielder.

Verdict: Bowling attack lighter than usual with Jofra Archer injured and limited availability for Rashid Khan and Jordan - but still very much in contention to top the group. MR

Bet365: 10/1