Basic rules of twenty20 cricket.
The basic rules and laws of twenty20 cricket are fundamentally the same as a one inning one day international cricket match. The rules of Twenty20 cricket matches state that each team in a twenty20 cricket match will have a maximum of 20 overs.
Other rules and laws are intended to make cricket more exciting and a thrill a ball.
 

The Free Hit
Following a no-ball, the next ball shall be a Free Hit. For this ball, the batsman is not given out by any way in the cricket rules, apart from being run-out.
 

Power to the Umpires
Umpires may award five runs to one of the teams should the umpires feel that the other team is needlessly wasting time.
 

Twenty overs within 75 minutes
Bowling teams are penalized for not completing their allotted 20 overs within 75 minutes. A bonus of 6 runs is awarded to the batting team in case the bowling team does not begin their 20th over before 75 minutes. This is to ensure that the match is completed within 3 hours; this has the TV and Sponsors in mind.

Bowling restrictions of Twenty20 cricket
A bowler can bowl a maximum of 4 overs. Rain shortened games will change the amount of overs a bowler may bowl.

Fielding restrictions of Twenty20 cricket

Twenty20 rules state that only 5 fielders can field on the leg side at any point of time.
The other fielding restriction rule states that a maximum of two fielders can be outside the ring in the first 6 overs and a maximum of five fielders can be outside the ring for the remaining 14 overs. This is similar to the fielding restriction rule of one day international cricket.
 

Bowl-outs
This special twenty20 rule applies to matches that end in a tie. This rule introduces the novelty of a bowl-out to decide on the outcome of the cricket match.

Five bowlers from either team are allowed to bowl two balls at the wicket with no batsman at the crease. The maximum times the wicket is castled by either team decides the outcome of the Twenty20 match.
 

More Twenty-20 Information