After the longest pre-season of their lives, county cricketers return to action on Saturday as the one-off Bob Willis Trophy gets underway with nine opening-round fixtures. Here, we run the rule over the contenders in each group…

North Group

Favourites: After a convincing batting effort in their pre-season friendly against Lancashire, Yorkshire look like the team to beat. Dawid Malan is fit after missing out on England's one-day squad through injury, while Jonny Bairstow looks set to play at least two games. Gary Ballance misses out through illness (he has had two negative Covid tests), but with Duanne Olivier available their seam attack should be strong enough to take 20 wickets regularly.

Contenders: Nottinghamshire have a number of players with points to prove, not least Haseeb Hameed, Joe Clarke and Zak Chappell. Durham were much-improved last year in finishing fifth in Division Two and after Paul Coughlin's return from Notts, they look to have one of the North Group's best seam attacks. Lancashire will be hampered by the absence of several players on international duty but can still compete, while Leicestershire and Derbyshire will rely heavily on the runs of Hassan Azad and Billy Godleman respectively. With only two Division One counties, the North Group looks like the weakest on paper.

Star man: Much loved by his own supporters but ignored by the England set-up, Ben Coad has taken 143 first-class wickets at 20.12 over the last three years and will be crucial to Yorkshire's push at the top of the group. He admitted to frustrations this week that he is not seen as a potential international bowler, citing Jason Holder's success as an example, but knows his control and patience make him one of the best seamers on the circuit.

One to watch: You would be hard-pushed to find anyone in county cricket who doesn't wish Haseeb Hameed well, and he showed positive signs in making 65 in a pre-season fixture last week in his first outing for Notts after his move from Lancashire. His return to Emirates Old Trafford on August 15 is a standout fixture.

Opening fixtures: Lancashire v Leicestershire (New Road), Derbyshire v Nottinghamshire (Trent Bridge), Durham v Yorkshire (Chester-le-Street)

Central Group

Favourites: After a strong showing in pre-season, Warwickshire look best-placed to win the Central Group and have Olly Stone fit and firing after a long build-up in England's Test bubble. Rob Yates will open alongside new captain Will Rhodes, with Sam Hain and Ian Bell the ideal men to push on from a solid foundation. There are a number of seamers in contention to play, and that depth could prove crucial with fixtures coming thick and fast.

Contenders: Somerset only just missed out on a maiden title last summer and have a deep enough squad to cover for international call-ups, but the batting looks a little light following Marcus Trescothick's retirement and with Tom Banton on England duty. Gloucestershire fell to an innings defeat against them this week but have a strong local core and added allrounder George Scott over the winter, while Northants are another underrated side who have retained their promotion-winning squad from last year. Worcestershire hope Jake Libby can address their red-ball batting struggles from recent seasons while Glamorgan will miss Marnus Labuschagne's runs with his contract deferred to next year.

Star man: Ryan Higgins tore up Division Two last summer with 958 runs and 50 wickets, and looks set for a middle-order role in addition to opening the bowling. That could be a mighty burden with little time for rest between fixtures, and it will be interesting to see if he can make the step up to playing a slightly higher-calibre of opposition - though all the signs so far are that he will flourish.

One to watch: One of only a handful of players overlooked for England's 55-man training group at the start of the summer who had been on the Lions tour, Tom Abell has grown into the Somerset captaincy and commands the respect of the dressing room. But he knows that a first-class batting average of 31.59 is too low to merit Test selection, and could do with a prolific season to shore up his side's middle order. His knack of breaking partnerships with his medium pace will come in handy, too.

Opening fixtures: Gloucestershire v Worcestershire (Bristol), Somerset v Glamorgan (Taunton), Warwickshire v Northants (Edgbaston)

South Group

Favourites: It is hard to see anyone other than Essex winning the South Group after their second Championship in three years last season. Ravi Bopara has moved on to Sussex and Dan Lawrence may miss the occasional game as a Test reserve for England, but with the same bowling attack raring to go they look certain to challenge. Simon Harmer missed this week's pre-season game but looks set to play.

Contenders: Hampshire would have been dark horses for the title before Covid, but with Nathan Lyon's deal off, James Vince and Liam Dawson on international duty, and Kyle Abbott and Fidel Edwards both stuck at home, their squad is significantly depleted. Kent added Jack Leaning over the winter but their batting looks slightly light with Joe Denly injured and Sam Billings on ODI duty, and Sussex will rely on all-round contributions with their squad stretched and Stiaan van Zyl and David Wiese both in South Africa. Surrey have the depth to cope without Hashim Amla and Morne Morkel - though Alec Stewart is lobbying his local MP for help with their visas - but struggled without Rory Burns' runs last year and will again be hampered by international call-ups, while Middlesex's seam attack is impressive but Nick Gubbins and Stevie Eskinazi will have to step up with the bat.

Star man: Jamie Porter reached out to the England selectors after missing out on their 55-man training squad and will be desperate to remind them how good he is with another strong county season. His partnership with Harmer has underpinned two titles already, and could well help them add the Bob Willis Trophy to Essex's collection.

One to watch: After expecting to focus on white-ball cricket this year, Mason Crane looks set to be Hampshire's frontline spinner. He has struggled with back injuries since his Test debut in the 2017-18 Ashes, and leaked runs last Championship season. But the prospect of five games in August and September - and Hampshire playing three out of five fixtures at outgrounds - should suit him, and with the format encouraging teams to go for wins, he could come into his own on the final day of games.

Opening fixtures: Essex v Kent (Chelmsford), Surrey v Middlesex (The Oval), Sussex v Hampshire (Hove)