Over my first two months at FanGraphs, I was surprised that the thing I got the most questions about was bat speed. Part of that may be that I’ve spent a lot of words talking about how mysterious the hit tool is, while bat speed seems like an input of the hit tool that’s objective. The common question is basically that, if this one part of the mystery can be perfectly quantified, then why aren’t scouts trying to demystify the process by quantifying it?
The problem is that bat speed can’t be perfectly quantified and there are maybe a dozen inputs to the hit tool. I split power into raw (deepest shot in batting practice) and game (homers per full MLB season at maturity) because of the obvious split between tools and game performance. A player could be “measured” to have plus bat speed but have no ability to make contact with that swing, like a pitcher that can hit 95 mph but has to pitch 90-92 mph to command it enough to stay in the game.