Notclay hit the nail on the head. A free, unimpeded armswing will get the feet going a little faster but gravity swings the ball pretty fast too. For bowlers who muscle the ball excessively, freeing up the swing takes a little trust and "courage" but once your muscle memory hard -wires it, a free swing is the way to go. You will become much more consistent shot after shot. Again though, without a video of your approach, it is difficult to pinpoint for sure what exactly is causing your flying trail leg.
A very common error I notice with a lot of bowlers is their tendency to rush the downswing as they are entering their slide step. Many good bowlers
will often pull the ball down from the top of their backswing instead of waiting for gravity to allow the ball to descend . This alone, will often result in an off-balanced delivery. I believe it was the great Carmen Salvino who said it best (about pulling down on the ball). He said that when a bowler pulls down (using muscle) on the ball, what they are really doing is attempting to bowl before it's TIME to bowl.
