Can a wicket keeper move after bowl reach to him for stumping? Will it be a fair delivery?
I think the rules relevant to your question are under 27.3 and 27.4 of the MCC rules here.
What I take from those is that:
- the wicketkeeper must remain behind the stumps until the ball strikes the striker or bat, passes the stumps, or the striker attempts to run. If this rule is broken, a no ball is called.
- in the time between a ball being bowled, and any of those 3 events occuring, the wicketkeeper cannot significantly alter their position. If they do, a dead ball is called. Exemptions to this rule are where the wicketkeeper is:
- taking a few steps forwards to respond to a slower ball, providing this does not bring them within reach of the wickets
- responding to lateral movement of the ball
- responding an action from the striker suggesting the shot they will play
I think the first exemption there is most relevant to your question. If a wicketkeeper was standing back, and then moves up to the stumps as the ball is bowled to effect a stumping - I believe the umpire should call a dead ball. Otherwise, if umpire considers the keepers movement to be legitimate, the stumping should stand.