In years past, I would have offered the panicked Tim Lincecum and Roy Halladay owners 50 or 60 cents on their draft-day dollars for their struggling former stars. But even though I intended to offer Hyun-Jin Ryu for Halladay in NL Tout after two starts, I didn't because Halladay's velocity was down. From 92 mph in 2011, to 90.6 last year to 89.7 in four starts this season.

Five years ago, I might not have known his velocity was down, and it would have been a basic "buy lowest out of principle" decision. But now I've learned to be cautious about pitchers with diminished velocity. After seeing Halladay pitch well against the Cardinals, and Lincecum (avg. fastball 90.4 mph) dominate the Padres, I think I might have been been better off not knowing.

The problem is we don't understand fully how gains and losses in velocity affect particular pitchers even if we know generally that more velocity - all things being equal - is better.

Tom Tango has an interesting post about this. In the comments he argues:

That fastball-speed/ERA relationship has a huge variation around it. That say 20|PERCENT| or 30|PERCENT| of pitchers who lose 1 mph in fastball speed has no effect on their true talent, while maybe another 20|PERCENT| to 30|PERCENT| has say a 1.00 ERA worsening. That's because of all the other things that could be linked to that.

Taking a general finding, and applying it to individual pitchers is, as I said, lazy, boring, and unenlightening.

This theory is actually borne out by what's happened so far this year. Jeff Passan of Yahoo! Sports, wrote about Justin Verlander losing fastball velocity - along with Felix Hernandez, Max Scherzer and Matt Moore - among others who are still pitching as well or better than ever.

Passan quotes anonymous scouts and baseball people (why they need to protect their identities is beyond me, and doing so greatly diminishes their credibility, but that's a topic for another post) who largely worry about the guys who are struggling, older, not as good or coming off of injuries (Sabathia/Halladay/Niese), but are not concerned about the ostensibly healthy stars like Verlander or Felix Hernandez ("I think he's evolving," one general manager said of Hernandez. "Less power, more pitcher.").

But of course the scouts are going to explain away velocity concerns when the results are good and going to hone in on them when the results (or career trajectory) is not. Should Halladay win his next four games, pitching like he did in 2010, I have little doubt many scouts will offer up their explanations as to why the loss in velocity doesn't matter for him after all.

The bottom line: whenever a pitcher performs poorly over a certain stretch, there will be cause for concern about his health or his skill set. Bad performance is often a leading indicator of future bad performance. The question is whether diminished velocity during bad performance is a better indicator than the performance alone. And if so, how much better? Also a few others: what kind of sample do we need to know whether the diminished velocity is permanent rather than temporary? Are there differently calibrated radar guns at different parks? What pitching repertoires suffer most as fastball velocity diminishes?

More data is always good, but until we understand it in proper context, it might do more harm than good when we decide to act on it.