This article is part of our Collette Calls series.
Wednesday afternoon, Peter Gammons tweeted out the following tidbit about Justin Masterson:
Justin Masterson's change in 2-seam and 4-seam usage w/ backdoor and back foot sliders why LHHs are .146/.222/.195/.417— Peter Gammons (@pgammo) April 17, 2013
Shortly thereafter, Ken Rosenthal tweeted out something very similar to which I replied that Masterson had been using his slider more frequently to left-handed hitters than he had historically done according to his pitcher card at BrooksBaseball.net. This then sparked a civil discussion back and forth with Joe Sheehan about sample size.
We know from the work that Russell Carleton, now of Baseball Prospectus, did years ago just how much of a sample size is needed for a stat to become meaningful. Both Sheehan and myself are rather familiar with that research and we both preach it frequently, even if one of us was singing the praises of Bryan LaHair 114 plate appearances into last season only to watch him have a .638 OPS from that point forward.
My point in the discussion was all change has a starting point. If a pitcher's strikeout rate needs 150 batters faced to become meaningful, it does not mean we ignore plate appearances 1 to 149. Rather, it means we watch the player's process during that span to see if something has changed or if the improved numbers are another example of statistical randomness. Last season, Fernando Rodney faced just 42 batters in April but had seven saves and a 0.87 ERA.