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Revisiting Diamondbacks Expected Offensive Statistics

Things could be worse

San Francisco Giants v Arizona Diamondbacks
Carson Kelly is awesome
Photo by Norm Hall/Getty Images

You’ve heard of wOBA and xwOBA before. For some they are familiar terms, for others they’re just more alphabet soup acronyms. I’ll try to make this as simple and painless as possible.

wOBA = Weighted On Base Average. This stat simply takes each way of getting on base and attaches a value to that on base event based on how much those events contribute to run scoring. Obviously in a context neutral situation, a double is worth more than a single, a single is worth more than a walk, a homer is worth more than anything, etc. A more detailed explanation including formula can be found HERE. But the summary simply says:

Why it’s useful

Unlike on-base percentage and OPS (OBP + SLG), wOBA assigns value to each method of reaching base, in terms of its impact on scoring runs.

xwOBA is the “Expected” version of wOBA. We’ve all seen a guy hit frozen ropes into the glove or hit a ball that gets windblown into the seats despite less than barreled contact. xwOBA looks at the quality of contact (Launch Angle + Exit Velocity) and measures what should or usually happens with that level of contact, as well as how HOW MUCH contact is being made. Detailed explanation and formula HERE

Simply put, if a hitters xwOBA is much higher than his wOBA, he’s probably been a bit unlucky and if he continues doing what he’s doing, his results should improve. On the other hand if the xwOBA is much lower than the wOBA, the hitter will need to increase the frequency or quality of his contact to maintain his level of results.

Important to remember, hitters aren’t static. The quality and frequency of the contact obviously changes for better or worse all the time. So xwOBA is not something you look at and say “That’s what he’ll hit going forward” BUT it is somewhat more predictive than wOBA itself, and it’s important to see who has been extremely over or under when evaluating a player.

One last caveat: League offensive environment changes from year to year. But Baseball Savant doesn’t update the formula on a daily basis to match with current league averages. Right now League Avg xwOBA is actually 10 points higher than actual wOBA. (.320 vs. 310) They’ll adjust that mid season or end of season. But for these tables I reduced the xwOBA by 0.10 across the board due to the current difference.

Below is the Diamondbacks team table, sorted by xwOBA. It’s color coded and shaded, Red = Hot, Blue = Cold. The difference column is color coded. The deeper the Blue the more the results have exceed expected, and the deeper the Red the more results have been under what should have been expected

Carson Kelly has been awesome. Hs xwOBA is the 2nd best in MLB ! While I wouldn’t expect that to stay there all year there is nothing flukey about the results he’s gotten so far.

Ketel Marte has hardly played. Small Sample Size caveats apply. His xwOBA is still very good, but he’ll need to improve his quality of contact to keep his numbers elite.

Asdrubal Cabrera was going well before he got hurt. But he was also exceeding quite a bit.

Pavin Smith has been a little unlucky in his results. This is a bright spot, as we should see his results improve.

Josh Rojas’ numbers don’t look that sustainable by this metric, unless his contact quality and frequency improve.

Eduardo Escobar has been pretty close to expectations. I don’t expect much different going forward

Kole Calhoun hardly played before getting injured again. Who knows what he’ll be doing when he comes back.

David Peralta almost always has higher wOBA than xwOBA. He tends to break this metric as he hits it on the ground so much. While some regression may be in order, don’t let his difference scare you too much.

Steven Vogt is what he is, an aging catcher in the last year of his contract.

Daulton Varsho: Good news, he has been the unluckiest guy on the team. Bad News, even if his luck was neutral he’d have a well below average wOBA

Josh VanMeter cannot claim bad luck for his poor results. He earned them so far.

Tim Locastro: See Josh Van Meter

Christian Walker: . See Tim Locastro

Nick Ahmed: WTF. Nick ?? As low as that wOBA is, xwOBA thinks he’s been lucky. Hopefully that’s not true !


The DBacks rank 17th in wOBA but 26th in xwOBA. So as bad as the offense has been the last 3+ weeks, dragging down all the numbers for the season they’ve actually gotten better results than they deserve. That’s um.....not great.

Obviously injuries have been a factor. But we all know that can’t be used as an excuse. All teams have had injuries. While I personally expect the offense to improve from the recent slump, my long term expectations are tempered, to say the least.