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.
So, knowing how fast a bat can move isn’t really helpful as an input to the hit tool and thus isn’t really useful. Exit velocity off the bat in a game could be useful as an objective measure, but suffers from the same problem of the eye-catching outlier data points possibly not being repeatable. Using average bat speed or exit velocity of hard contact in games could be useful, but then you’re mixing funky, off-balance swings with ideal swings and that isn’t really answering a question, either. Maybe we could use one of these?
Scouts put bat speed in buckets. Roughly speaking, there’s below average, average, above average to plus and elite. Most teams don’t ask their scouts to formally grade it on the report, so it’s more of a thing you casually mention in the comment next to the grade. Fans can normally put players in the correct bucket, though I’ve noticed fans and scouts will disagree more than usual when a big slugger is the player in question (Dan Vogelbach is the example at that link), as the big body can sometimes play tricks on your eyes. While this could be an instance where measuring bat speed could be more useful than the bucket system, more precise information still likely wouldn’t change the hit tool grade in the end.
Scouts are just trying to line up the inputs of the hit tool and see what the overall picture is, with bat speed the great equalizer: you can get away with worse inputs if you have elite bat speed and everything has to be perfect if it’s fringy, just like defense and foot speed for a center fielder. Being more certain that one guy has 55 bat speed rather than a 50 doesn’t really change this math and I don’t think scouts are missing by more than 5 points with any regularity.
Another example that’s harder for fans to notice is when a guy generates above average bat speed in a small area, with Cuban free agent Yasmany Tomas as an example that tripped up some readers, with the big body issue also complicating the issue.
Someone asked in the comments of my Tomas report why they don’t see above average bat speed here and this was my answer:
Tomas generates above average bat speed but doesn’t load his hands as far back as most sluggers. Almost all power hitters load their hands (maximum distance from contact) about as far back as possible (for a RH hitter that means stretching his left arm as far to his right as possible) or close to it, and Tomas doesn’t do this. This means he has the power and bat speed of a big-time power hitter with the short bat path of a contact hitter. This is what I mean by the tools to hit and hit for power in games, even if he hasn’t been showing it lately due to plate discipline issues.
This is rare because Tomas is one of the guys that’s quick-twitch in his hands (he accelerates them very quickly and smoothly) but isn’t quick-twitch in the rest of his body. Most baseball fans are used to seeing big bat speed in a quick-twitch body that could be a football star and is plus at everything (Adam Jones, for example) but it’s harder to notice that in more of a fullback-type body when the rest of the body isn’t also quick-twitch.
Hitters like Gary Sheffield or Javier Baez that have 80 bat speed normally have longer bat paths (designed for timing, because their bats move so quickly and thus can get out of sync easily) which makes it easier to notice their bat speed. Tomas’ hands just move more quickly than you’d expect in a 12-18 inch area, which is hard to notice when the body doesn’t scream quick-twitch and you aren’t watching tons of swings every day from this angle.
So, no, you aren’t some sort of idiot for not immediately realizing this. It may be good that you haven’t seen hundreds of minor league lifers with slow hands so that this guy jumps out.
There are some players where scouts may tend to over/underrate their bat speed by a notch and there are some players that are harder for fans to put in the right bucket. It’s still a hit-and-miss, mysterious tool to evaluate, but, in a broad sense, the system that scouts are currently using for the hit tool doesn’t have a big hole to be poked in it.
Kiley McDaniel has worked as an executive and scout, most recently for the Atlanta Braves, also for the New York Yankees, Baltimore Orioles and Pittsburgh Pirates. He's written for ESPN, Fox Sports and Baseball Prospectus. Follow him on twitter.