Interesting article on Yahoo: http://sports.yahoo.com/mlb/news?slug=ap-behindthestats&prov=ap&type=lgns

Great stuff: The most unhittable pitches in baseball
By TOM KOCH-WESER, STATS Analyst

Phillies GM Pat Gillick recently said Cole Hamels, his prized 23-year old southpaw, had the best changeup he'd ever seen from a left-hander.

Not exactly a source of objectivity, Gillick's statement might otherwise be dismissed as reeking of bias from a proud boss.

But what if he's right? And how can we tell?

Scouts often speak of pitchers with "plus" or "plus-plus" offerings, usually referring to where a particular pitch falls on the 20-80 scouting scale in terms of both velocity and movement. But if we dig a little deeper, which pitches - given their speed, movement and deception - are actually the most unhittable in the game?

While there's no exact way to measure a pitch's "nastiness," we can come close to quantifying it by assuming a basic baseball tenet: In almost all cases, the most ideal outcome for a pitcher on a given pitch is to have the hitter miss. As such, we can measure great stuff by using the "Whiff Rate".

The Whiff Rate is simply defined as the total number of swings and misses over the total number of swings. Assuming that the primary goal of a batter is to make contact, we can use this ratio to see who has the best "out" pitch - and to find out what it is.

Assuming a minimum sample size of 200 swings for fastballs and 100 swings for anything off speed, we can see who coaxed the highest percentage of whiffs a season ago. And, as it turns out, Gillick might not be far off in his assessment.

Hamels consistently delivered the most unhittable changeup in 2006, producing a Whiff Rate of .514, the leading figure by a significant margin over Colorado closer Brian Fuentes, who posted a rate of .460, and Arizona's Brandon Webb (.454).

Johan Santana, widely considered to have the best change in the game, finished the year at .450, fourth among qualifiers. To his credit, Santana also delivered his changeup more frequently in the strike zone (38.6 percent) than anyone in the top five, while opposing hitters slugged a meager .221 against it, also the best of the group.

Hamels' teammate, Ryan Madson, ranked fifth at .426.

While those players are certainly dominant when it comes to the premier off-speed pitch, the mantle of the most unhittable pitch in 2006 goes to the slider of Fernando Cabrera.

Cleveland's young reliever recorded a Whiff Rate of .652 on that breaking ball, and, if you think that's a fluke, think again. Had Cabrera qualified the year before, 2006 would have been the second consecutive season his slider led the league. In 2005, Cabrera posted an eye-popping Whiff Rate of .762, though in limited action (42 swings).

Interestingly, Cabrera only threw his slider in the strike zone 28.6 percent of the time, well below the major league average of 41.6 percent. In other words, he makes the pitch unhittable with a late bite that places the ball outside the plate or in the dirt much of the time.

Houston reliever Brad Lidge, recently demoted from the closer role, was once as dominant as any pitcher in the game with a slider that pushed his rate of strikeouts per nine innings to nearly 15 in 2004. While he's struggled mightily over the past year, his trademark offering is still effective with a Whiff Rate of .594, second behind Cabrera.

That rate also stands up as the second-most dominant pitch of any type overall. In fact, sliders make up the top three Whiff Rates from 2006, as the Cubs' Scott Eyre is third at (.515), just ahead of Hamels' changeup. Florida's Jorge Julio (.503) and the Cubs' Michael Weurtz (.503) round out the top five sliders.

But enough about secondary pitches. The most basic - and important - pitch in baseball is the fastball.

If we were to think of the hardest throwers in the game, Detroit set-up man Joel Zumaya would be one of the first to come up. His average heater hit a league-high 98.6 mph and he notched triple digits on the radar gun more routinely (261 times) than anyone else in '06. But does that velocity translate to missed pitches?

Indeed it does - although there were a select few that threw fastballs that were even tougher to get wood on.

For the second consecutive year, Arizona closer Jose Valverde led the majors in fastball Whiff Rate, posting a .315 in 2006. There's clearly something deceptive about Valverde's short, stabby arm action and low arm angle, visual features that only add to the difficulty of making contact with an explosive 94 mph four-seamer.

Valverde also threw 54.5 percent of his fastballs in the strike zone, a higher percentage than any of the top five fastball Whiff Rate leaders and well above the league average of 51.1 percent.

Perhaps the most interesting entry on the list is Chris Schroder, by any other means an also-ran reliever in the Nationals system who is currently pitching for Triple-A Columbus. Yet Schroder had the second-highest fastball Whiff Rate in the league last year at .313. Schroder has a similar arm action to that of Valverde's, but, interestingly, throws 3 mph slower (90.5), a velocity that is almost perfectly league average.

Dodgers closer Takashi Saito (.306) ranked third, trailed by the Mariners' J.J. Putz (.293). Zumaya (.275) rounded out the top five.

Another Cabrera tops the list when it comes to curveballs. Baltimore's Daniel, who throws the hardest power-curve in the game at 84.7 mph, also possesses the one that's most difficult to hit (.513 WR). We see a correlation between speed and Whiff Rate when it comes to the curveball, as fellow hard-throwers Francisco Rodriguez (.494) and A.J. Burnett (.453) come in at No. 2 and 3.

Two of the premier sinkerballers in the game, Webb and Derek Lowe, prove that a solid complement to a good sinker is a good curve as those two trail Burnett at .438 and .397, respectively. Webb, the NL Cy Young Award winner, was fittingly the only pitcher to appear in the top five for two different pitches.

So the next time a player, manager or GM comes up with seemingly exaggerated accolades for a pitcher's stuff, don't just take it at face value. A little analysis will most times prove it's just hollow praise. But sometimes, like in the case of Hamels, he just might be telling the truth.