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Fixing OPS’s Flaw


A commenter on this post about MLB No. 2 hitters noted that “For a #1, 3, 4, or 5 hitter a .725 OPS would be pathetic.”

Now, as I’ve said before, I’m no quantbot. But if a number like .725 is pathetic, OPS is not a useful stat. Let me explain — and offer an alternative or two.

The reason we track slugging and on base percentages in the first place is that batting average is a suboptimal measure of a hitter’s performance.

A guy goes two-for-four in five plate appearances. His BA is .500. But he also walked, and to reflect that one-base contribution to his team’s offense, we note that his OBP is .600. Now one of two hits was a double, so we note that his SLG is .750 to reflect the fact that he earned three bases in his four at-bats. OPS is an attempt to incorporate in one stat, using other readily available stats, the total value of the bases a player earns per plate appearance — that is, to capture both varieties of earned bases that BA misses. 

Unfortunately, BA is incorporated into both OBP and SLG. The most flawed offensive stat — whose insufficiency is precisely what called the other two stats into existence — is counted twice in OPS. Note: the imaginary player referenced above earned four bases in his five plate appearances. And yet his OPS is 1.350.

Consider last year’s OPS leader: Josh Hamilton at 1.044 (nudging past Miguel Cabrera at 1.042).

In 518 ABs, Hamilton had 186 hits (BA: .359) — comprising 111 singles, 40 doubles, 3 triples, and 32 homeruns (SLG: .633) — 43 walks, 5 hit-by-pitches, and 4 sac flies (OBP: .411). In terms of bases earned, that’s 111, 80, 9, 128, 43, 5 — 376 bases (328 from hits, 48 from non-hits) in 567 OBP-reckoned plate appearances, for what I’ll call an Earned-Base Average of .663. Nowhere near one base per plate appearance.

Compare Miguel Cabrera: In 548 ABs, he had 180 hits (BA: .328) — comprising 96 1Bs, 45 2Bs, 1 3B, and 38 HRs (SLG: .622) — 89 BBs, 3 HBPs, and 8 SFs (OBP: .420). That’s 96, 90, 3, 152, 89, 3 bases — 433 total — in 648 PAs, or a .668 EBA. In every three at bats, the big guy gets you a little over two bases. A shade more than Hamilton, in fact.

Now, it’s kind of a pain to calculate earned bases this way.

EBA = [H - (HR + 3B + 2B)] + 2B*2 + 3B*3 + HR*4 + BB + HBP / AB + BB + HBP + SF

A quicker way than EBA to compensate for the double counting of a hitter’s singles in OPS is to use what I can Single-Limited OPS, or SLOPS:


Or to look at it another way: subtract the batting average from the slugging percentage to isolate the non-singles component of slugging, and then add that to the on-base percentage, which already includes batting average.  


Tags: MLB


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