Jonny Bairstow is among the players to have been replaced this season. Rules allowing replacement players in the County Championship could be changed at the end of the first block of fixtures.

The England and Wales Cricket Board's (ECB) decision to permit replacements for injury, illness and significant life events has come under scrutiny after two weeks of the season. Nottinghamshire head coach Peter Moores said the regulations need "tightening", while Glamorgan captain Kiran Carlson said they need to be "ironed out".

Each of the 18 counties plays six fixtures and has a bye week in the Championship by the middle of May, at which point the competition breaks for the T20 Blast. The ECB sees this as the fairest and earliest time to make changes if they are required.

The implementation of replacements is being trialled across the 2026 season, and the trial will not be scrapped midway through the year. There have been nine instances of players being replaced across 18 matches so far, though one of those - Adam Finch of Worcestershire - was for a concussion, for which replacement rules were already in place.

Announcing the changes at the beginning of the season, the ECB estimated replacements would be required in about 25% of fixtures. After only two rounds of matches, the remaining games in the run-up to the break will give more opportunity to see how replacements have affected the Championship. The ECB has not received any official complaints over the replacements that have been used so far this season.

The trial follows similar experiments in domestic cricket in India, Australia and South Africa after the International Cricket Council asked members to test the use of fully participating substitutes with a view to an introduction in Tests, something previously only allowed for concussion and Covid-19. The ECB has taken the trial a step further than those countries by allowing replacements for significant life events, such as bereavements or the birth of a child, as well as injury and illness.

Replacements can come into the match at any point from after the first ball to before the last. In the case of injuries, replacements must be signed off by the match referee in conjunction with the club medical staff. Replacements for life events - not used so far - have to be agreed by the county chief executives of the two teams.

Replacements have been used in five of 18 matches so far, although in three of those matches the rule was used twice. Most complaints have been around the strictness of the rules, rather than the principle itself or specific cases.

Somerset coach Jason Kerr said Tom Kohler-Cadmore was unable to hold a bat and Lewis Goldsworthy had a severe hamstring tear after their injuries last weekend, while Yorkshire seamers Jhye Richardson and Jack White had food poisoning. Moores said seamer Fergus O'Neill was unable to bowl on the final day against Glamorgan but was already down on pace the previous day. O'Neill was replaced by Lyndon James, who took two wickets in a 192-run win.

Glamorgan's Carlson said his complaints were "no slight on Notts whatsoever". "A guy who hadn't played cricket for three days to then come in and bowl, obviously that's an advantage," he added. "The thinking behind bringing in the rule is sound, but I think it has to be ironed out in terms of the way it does get done."

The ECB has implemented more relaxed restrictions than other nations. It wants to keep the quality of cricket high by not having players with serious injuries struggling through matches - as seen with England's Chris Woakes in the fifth Test against India last summer.

In Australia the 'stand-down period' - the period a replaced player is then unavailable for - during the most recent season was 12 days, but in the UK it is only eight. There is also no stand-down period for players whose team do not play in the next round of fixtures - as is the case with Nottinghamshire, Glamorgan and Yorkshire this week - or for the final round in a season.

The Australian laws also only allowed one substitute per match and ruled that any change had to be made before the end of day two, thus reducing the advantage of a fresh player coming into a four-day match late on.

When explaining the rules last month, ECB head of cricket operations Alan Fordham said the governing body would be relying on the co-operation of the counties in not pushing the rules to gain an advantage. "If teams are going to start pushing at the edges of the regulation then it risks the chance we will have to backpedal," he said.

Former England wicketkeeper Sam Billings, who is currently playing in the Pakistan Super League, has been the most stinging in his criticism, calling the law "ridiculous".

Former England coach Moores said he expects the laws will be refined at the end of the season, agreeing that players coming into a match late is an issue. "There will need to be some tweaks to make sure it is tight," Moores said. "To have two in this game, we want to make sure that it doesn't become a focus for the season when we want it to be on the cricket. "There is a case for a tightening what point in the game can it be done."

Kerr said: "If someone is genuinely injured and they can't do the job they are selected to do, it is a good thing. "You could find ways to manipulate the system and use it to your advantage, and that does concern me. I won't be doing that."

Kerr said replacements for illness or soft issues injuries may need to be "tweaked". "I can think of games last year where we didn't select players because their partner was expecting," he said. "It means they missed the game and there were times the baby didn't arrive. "If you can mitigate that and replace them, that looks like a win-win that is common sense - similar from a bereavement point of view."

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