I want to know why the inner circle in limited overs cricket is drawn 30 yards from the wickets.
- Is there any logic behind it, or is that just the way it is?
- How does this work during power-plays?
In non limited overs cricket (i.e. 5 day test match cricket or 4 day 'First class' cricket), there are almost no restrictions on where fielders can be positioned, the only restriction being a limit of two players behind square on the leg side. You will sometimes see situations in which every fielder, apart from the wicket keeper, is on the boundary. This is sometimes known as a 'ring field'. Typically you would see this if a top order batter is batting with a tail-ender. The bowling team wants to stop the batter scoring boundaries, but are happy for them to score a single bringing the tail-ender on strike who they have a better chance of getting out.
The inner circle was introduced in limited overs cricket in order to stop the bowling team setting these kinds of very defensive fields for long periods, which makes the game boring. Without any restrictions, the fielding team could set all the players back to stop boundaries which makes for boring cricket. For instance, see this description about what used to be possible in one day cricket before fielding restrictions were introduced.
The way the inner circle works is that a certain number of players (the exact number differs between 50 over and 20 over cricket) must be within that circle. This means that there will always be some gaps on the boundary that the batter can target with attacking shots. In powerplays, the number of fielders that must be in the inner circle is increased, meaning even more gaps in the outfield giving the batter the incentive to hit the ball in the air over the top of the infield into the gaps, or even to try and hit a 6 knowing that if they miss hit it there are less outfielders who might be able to catch it.