This is the statement that makes me doubt this whole thread. a 5'10" 9 year old girl that throws 50? "a lot of 10 year old pitchers in tourneys that throw 50-52 with great consistency?" Either this is complete BS or someone is using the metric system accidentally. I don't doubt that there is the occasional phenom out there that is throwing mid 40s at 9, but this whole thing just screams troll/BS to me.
The #1 pitcher from Los Alamitos 8U All-Stars was throwing 48-50 (on radar, 10" ball @ 30') last Summer. We saw a couple other 8U pitchers during the All-Star season that were not far behind. Those girls are out there.
At the 10U pitcher evals for our league last weekend, we had a 9yo and a 10yo each hit 44 (on radar), with others at 42-43. These girls will get faster as we head into the Spring season.
I do agree that using a stopwatch to calculate velocity is prone to a LOT of error.