Stride leg position at release?(Bent or Straight)

:?: My son is 13 and has learned under the Tom House ideal for the past couple of years. At release he throws out over his front knee(bent).I have noticed that most pro pitchers lock there front knee at release to facilitate hip rotation. I was wondering if anybody has an opinion on this topic because we are considering changing his delivery to a more stiff legged at point of release.

In terms of the pros, it’s 50/50 bent versus locked.

I prefer bent for a variety of reasons, including that when it comes to the greats you seem to see more bent front legs than locked front legs.

Why are you considering this change? Just because you think it’s what the pros do? Do you think there is something wrong with the House approach? If there is some problem you’re trying to address, are you sure the front leg is the issue?