this is not common practice far as I know in my league, I suspect as has been pointed out it would be a guaranteed flashpoint for the fielding side or the bowlers would start just running out batsmen 'backing up' which has been covered to death on the forum so let's no go there
having not really considered it myself this is my question: is the ball live as soon as it leaves the bowlers hand? so you can start legging it then?
the reason I ask is because im sure everyone knows current stumping rules prevent the keeper taking the ball until AFTER it's passed the stumps at the strikers end.
Def seems double standards to me, if batters are taking a run to the keeper.....