In a first for a major T20 competition, the Big Bash League has introduced three major rule changes this year: the Power Surge (the usual six-over powerplay split into four overs at the start of an innings and a floating block of two for the batting team to call in the second half of the innings), the Bash Boost (a bonus point for the team with the higher ten-over score) and X-factor replacements (the option to bring in a substitute player after ten overs of the match). What impact have they had on how the game is played?

New-ball impact

Perhaps the most significant feature of the BBL season to date has been the success that new-ball bowlers have had, which has in turn impacted the changes in the powerplay's structure. With the initial powerplay reduced to only four overs rather than the usual six, teams have scored at a sedate 6.61 runs per over in that phase of the game, despite only two fielders being permitted outside the 30-yard circle.

James Faulkner, the medium-fast left-armer, has been the most destructive quick with the new ball, taking four wickets in the first powerplay in six overs and demonstrating that pitches have offered something for the seamers early on, with good carry and bounce as well as some seam movement. As a result, teams have generally found themselves struggling for early runs, and many have tried to minimise damage rather than maximise scoring in the first four overs.

The fourth over in particular has seen scoring rates plummet to 6.23 runs per over, often due to No. 3 or No. 4 batsmen looking to get into the middle overs unscathed following early wickets. Other over-by-over trends have included a significant spike in 15th-over run rates - largely due to the Power Surge being taken - plus a rise in the 11th and a fall in the 20th. The sample size is very small, so it is not worth reading too much into them at this stage, and the data also includes rain-reduced games.

To surge or not to surge?

The majority of teams batting first have looked to use the Power Surge when they have two set batsmen at the crease to maximise their scoring, and have looked to use it to give their innings some impetus before the traditional 'death' overs. In the first innings, the most popular time to take the Surge has been the 15th over (four times), with teams also taking it in the 12th, 14th, 16th, 17th and 19th on one occasion each.

In run chases, there has been less of a pattern. Two teams have not taken the Surge at all in the chase: Melbourne Stars, when cruising to victory against Brisbane Heat, and Melbourne Renegades, who were bowled out after 10.4 overs against Sydney Sixers, while Adelaide Strikers held theirs back as long as possible in their comfortable win against Hobart Hurricanes.

Generally, teams have been more cautious in using the Surge in the run chase, perhaps fearing that it will upset the flow of the game by forcing both teams to attack. In the season opener, the Sixers made 18 without losing a wicket in their two Surge overs, but having scored 69 for 0 in the seven preceding overs, that actually represented a slight slowdown, not least after James Vince had hit the first ball of the Power Surge for six.

"The Surge and when we took it, from a batting point of view, maybe changed the momentum a little bit," Vince said after the Sixers' eventual defeat. "I thought their guys bowled two good overs, and it gave them a bit of a lift… it kind of got them back into the game."

Conversely, Sydney Thunder timed their Surge brilliantly against the Heat, with Ben Cutting and Daniel Sams exploiting the field restrictions to take 27 off two overs. That turned the required equation from 77 off 42 balls into a significantly easier 50 off 30, and they went on to win with seven balls to spare.

Overall, teams have scored an average of 10.24 runs per over in the Surge, losing a wicket every 10.5 balls, with spin (12.4 economy rate) significantly more expensive than seam (9.73). The Sixers have made the highest total in the Surge to date, with 32 for the loss of one wicket against the Renegades.

Bonus point bonanza

Chris Lynn admitted on air that he hadn't thought about the bonus point during the Heat's comprehensive loss against the Stars - when the point was all they could really have hoped for - but the Bash Boost has played at least some role in how chasing teams have gone about things.

The Renegades' blow-out defeat against the Sixers saw them actively and openly targeting the bonus point, with a target of 76 after ten overs looking significantly more achievable than 206 in 20 once they had slipped to 16 for 3 after 2.4 overs. They were ultimately unsuccessful, but their players and coaching staff maintained that their plan was a good one.

"How often do you see teams chasing a really high score when they're 20 for 3 after three overs?" said Benny Howell. "You might look bad if it goes wrong and you're bowled out early, but you still lose the game, and at least you're trying to get something from it. I think it was the right decision, we just didn't execute at all well."

Meanwhile, the prospect of a bonus point seemed to influence the Thunder's thinking in their chase against the Heat, even though they ultimately fell short. From 23 for 3 after three overs, their first target was 80 after ten overs for the bonus point, and 99 more in the final ten overs.

Rather than consolidating and hoping to take the game deep, the injured Alex Ross decided to swing for the hills once the ten-over mark was in sight, leaving nine required off the tenth to seal the point. Mujeeb Ur Rahman then bowled a tight over for the Heat, taking a wicket and conceding only two runs, but the attacking mentality instilled by the halfway target meant the required rate was never unassailable.

In the first nine games, the point has gone to the winning team six times, the losing team twice, and been shared once - in the no-result between the Stars and the Scorchers.

Will X-factor become a factor?

The first seven games of the season saw no X-factor players used, perhaps due to conservatism among captains and coaches, or maybe on account of the collective unavailability of several overseas signings and Australia A players, meaning the nominated 12th and 13th players were often grade cricketers.

In the eighth game, both the Strikers and the Hurricanes used a substitute to bring in a batsman for a spinner on a pitch that was not conducive to spin: Matthew Short for Danny Briggs, and Mac Wright for Johan Botha. In the ninth, the Stars did the same after their rookie legspinner Tom O'Connell's first over was smashed, deciding to back the part-time left-arm spin of Nic Maddinson and strengthening their batting through Ben Dunk.

It remains to be seen whether replacements now become commonplace. Their timing in the match means that teams have to admit making a mistake in selection very early in a game: while substitutions are regular in other sports, the timing is equivalent to a football manager taking a player off inside 25 minutes.

And while squad depth may be less of an issue as the season goes on, it may be that this rule is better suited to a competition with significantly bigger squads. It is easy to imagine Sunrisers Hyderabad bringing Mohammad Nabi in for Jason Holder after realising a pitch was slower than anticipated, for example, but the impact that a fringe local player will have on a game is likely to be negligible.

The early verdict

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What is the thinking behind the BBL's new rules? Trent Woodhill tells us
What is the thinking behind the BBL's new rules? Trent Woodhill tells us

Speaking to ESPNcricinfo's Newsroom, Trent Woodhill - the BBL's player acquisition and cricket consultant, and the man behind the tweaks - clarified that the intention was to avoid "lull" periods in the middle overs, maintain fans' interest even in one-sided games, and provide extra scrutiny on coaches and captains in their decision-making.

Clearly, it will be easier to form a judgement after a full season rather than the first week of games, but the rule changes have been a qualified success in creating talking points and making the pattern of T20 games less predictable than spikes in run rates at the start and end of an innings. On one hand, the middle overs have generally provided more excitement, with middle-order batsmen given additional responsibility and the chance to attack in the Power Surge; on the other, the initial four-over powerplays have generally been quieter and more predictable than the old six-over version.

There is some reason to believe that the rules will come into their own as the BBL goes on. Bonus points should reduce the likelihood that net run rate will decide qualification and potentially throw up some intriguing scenarios, while improvements in player availability could bring the X-factor replacements into the picture. The rule changes alone were never likely to arrest the slump in interest in the BBL, but they have certainly added intrigue and altered the rhythm of the game as intended.

Matt Roller is an assistant editor at ESPNcricinfo. He tweets at @mroller98