This metric evaluates a pitcher based on how many hits and walks he allows per innings pitched. It’s pretty easy to calculatea pitcher’s WHIP. Assuming our friend Randy Johnson gives up 6 hits and walks 2 batters in 7 innings pitched, his WHIP would be: [2 (walks allowed) + 6 (hits allowed)]/7 (innings pitched)= 1.14.
WHIP typically correlates to ERA in that both will be high or both will be low for a given pitcher. Theoretically, the more Walks + Hits per Innings Pitched, the more earned runs that pitcher stands to give up. However, WHIP does not statistically account for earned runs. The end result of this, though unusual, is that a pitcher can indeed have a high WHIP and a low ERA or vice versa. This is an extremely important concept to understand, as it often times can be a great tool for isolating overvalued or undervalued pitchers.
For example, the Dodgers Kaz Ishii currently has a nice 3.49 ERA. Those studying just ERA may feel good about Ishii moving forward. A closer look, however, reveals that Ishii also carries a dangerously high 1.49 WHIP. Why the discrepancy? Well, Ishii's currently second in the Major Leagues with 44 walks allowed. That is an alarming number of base on balls—base runners—he is putting out there. Thus far, the walks have not come back to haunt Ishii in the form of runs. But rest assured, if Ishii continues to issue free passes it will start to impact his ERA as well. So in this particular instance, Ishii’s strong ERA may in fact be misleading given his comparatively high WHIP.
So as a frame of reference, here is MLB’s Average WHIP, MLB’s Median WHIP, the NL’s Average WHIP and the AL’s Average WHIP. All as of June 1, 2004.
MLB Average 1.41 WHIP
MLB Median 1.36 WHIP
NL Average 1.37 WHIP
AL Average 1.45 WHIP
So far evaluation purposes, a WHIP below 1.41 would be factored as better than average. The lower it goes, the better the WHIP becomes. The reverse obviously holds true as well. The higher the WHIP, the worse.