Expected stats give us different kind of X-factoron April 26, 2021 at 11:27 pm

Early-season stats can be a bit wonky, thanks to extremes born of small sample sizes.

The White Sox’ Yermin Mercedes has been amazing, leading the majors with a .414 batting average and ranking fourth with a .477 weighted on-base average (through Sunday). The Cubs’ Ian Happ has been slow out of the gate with a .154 batting average and a .261 wOBA. The major-league averages are .232 and .308.

We can expect time and hundreds of plate appearances to lead to slopes down for Mercedes and up for Happ. For the time being, we can look a little deeper with expected stats.

Expected stats change the question from ”What results has a player achieved?” to ”What results would we normally expect from a player’s quality of contact?”

Fangraphs.com player pages and expected stats leaderboards at baseballsavant.mlb.com list xBA, xSLG and xwOBA, with the ”x” standing for ”expected.”

If a batter bloops a ball that would be a base hit only 12% of the time, that’s 12% of an expected hit. If he’s robbed by a diving catch on a ball that would drop safely 92% of the time, he has an expected 92% of a hit.

The ”x” stats weigh exit velocity and launch angle. On some balls in play, sprint speed is taken into account. The Sox’ Luis Robert, with a sprint speed of 28.5 feet per second, has a much better chance of turning an infield nubber into a hit than Yasmani Grandal at 22.7 feet per second.

With all that factored in, along with strikeouts for xBA and xSLG and strikeouts and walks for xwOBA, Mercedes still comes across near the top of the class.

Mercedes’ .328 xBA is 86 points lower than his batting average, but it ranks 22nd in the majors. His .657 slugging percentage ranks 12th and .632 xSLG 27th, and his .477 wOBA ranks sixth and .417 xwOBA 25th.

There’s a gap between Mercedes’ results and the results his quality of contact normally would generate, but maintaining his expected numbers would be reason to celebrate.

As for Happ, his .154 batting average ranks 269th among major-league qualifiers, his .200 slugging percentage 284th and his .261 wOBA 226th.

But Happ’s average exit velocity is 90.6 mph, 43rd in the majors. Expected stats suggest he has hit the ball better than his results show. Happ’s xBA is .210, his xSLG .384 and his xwOBA .334. That above-average xwOBA is fueled largely by his 15 walks, tied for eighth in the majors.

Among other Chicago players, the Cubs’ Kris Bryant has better results but still strong expected results, with a .292 batting average, .597 slugging percentage and .411 wOBA vs. a .261 xBA, .504 xSLG and .357 xwOBA.

The Sox’ Jose Abreu’s early results are a near-match for his ”x” stats, with a .225 batting average, .438 slugging percentage and .325 wOBA vs. a .235 xBA, .478 xSLG and .332 xwOBA.

Samples will get larger. Hot and cold streaks will smooth out the averages. In the meantime, stats based on quality of contact give us extra information about player performance.

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