Instead of blaming the bowlers or Dhoni, this idiotic rule must be blamed which is making a mockery of cricket. If you go through the match, a match which is supposed to be of 50 overs a side gets reduced to just 21 overs for Srilanka. If you go by the results of T20 then you can find that this score is easily gettable. So actually the rule is the main problem. There must be a minimum limit for the no. of overs to be bowled.
