Does anyone roughly remember how much velocity was lost when pitchers transitioned from the 50x70 to 54x80 to 60x90? I can only assume that if you take the same kid and have him throw from 50 feet it's going to be faster than 60 feet.
Technically, velocity is not lost. If a kid throws 75 from 50', he will still be throwing 75 from 60'. What does happen is that as a pitch travels, it loses velocity. I have read that the faster you throw, the longer it takes to lose velocity. It's something like a 98 mph fastball will lose velocity at the rate of about 1 mph every 7 feet. A 62 mph pitch will lose about 1 mph every 4 feet. Radar guns calculate velocity as soon as it leaves the hand, so if a kid can throw 75, he throws 75. However, how fast that pitch is still traveling by the time it reaches the plate will be less at 60' than at 54'