Brad Lidge is a two-pitch pitcher. His arsenal consists of mid-90s fastball and a high-80s slider. From 2008-2009, Lidge faced a few hundred 0-2 and 1-2 counts in which he had to choose a putaway pitch. While Lidge generally splits his pitch selection right down the middle, in situations when he's well ahead of the batter, he goes to his slider over 60% of the time. And he gets results.
PITCHf/x analysts like to use a metric called run value to assess the value of a pitch. Basically, you control for the count and measure the change in run expectancy for a given pitch. So for Lidge, his fastball has been worth a negative 1.5 runs per 100 pitches, while his slider has been worth a positive 1.5 runs per 100. In these 0-2 and 1-2 situations, the trend is similar. So why does he throw fastballs at all if the slider is his bread-and-butter?
Well, we don't really care about the result of the pitch as much as we do the outcome of the at bat. So how did Lidge ultimately fare at the end of each plate appearance?
Turns out, Lidge's fastball wasn't ineffective. In a way, it was more effective than his slider. That 57% ball rate might be intentional. Perhaps his advantage in the count allows him to use his fastball as a setup pitch.
Against righties, Lidge threw 50 fastballs that resulted in a prolonged plate appearance. He proceeded to strike out over half of these batters and allowed only six to reach base. Of course, any pitcher's numbers will seem otherworldly when the context is restricted to two-strike counts, but as Dave Allen has shown, a fastball generally makes for a better setup pitch than a slider.
How Lidge's slider works off his fastball.
Whether or not Lidge tries to raise the eye level of the batter with his mid-90s fastball, when his heater goes for a ball, it's the perfect setup for his slider.
While some pitchers' off-speed pitches exhibit superior run values, the fastball's grunt work may be the driving force behind such off-speed success.