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What to expect from San Francisco Giants rookie Mac Williamson

Jake Roth-USA TODAY Sports

Last night the San Francisco Giants placed infielder Ehire Adrianza on the disabled list with a broken foot, promoting outfield prospect Mac Williamson to replace him on the roster. Drafted in the third round in 2012 out of Wake Forest University, Williamson has been on prospect lists for some time and had a brief trial with the Giants in 2015. Let's take a look.

First, the basics from the 2016 Baseball Prospect Book:

Mac Williamson, OF, San Francisco Giants
Bats: R Throws: R HT: 6-5 WT: 240 DOB: July 15, 1990

2013: Grade C+; 2014: Grade B-; 2015: Grade B-

Giants fans really want Mac Williamson to develop into a regular outfielder. Finding flycatchers who can hit has been one of the few weak points in the system in recent years. On the right day Williamson looks like the guy, showing power to all fields and the willingness to work a count and take a walk. On the wrong day his bat seems to slow down and his swing gets tied up, usually when he tries too hard to pull, resulting in strikeouts. He runs pretty well for a big guy and can handle either outfield corner. Williamson is 25 now so he’s not young as prospects go, but I wouldn’t overlook him. He’s likely more good role player than long-term regular but he could hit .250-.260 with enough power to be useful. Grade C+.


Williamson hit well in spring training (.298/.388/.614 in 57 at-bats) and was hitting decently in his first week of Triple-A play, batting .276/.300/.552 in 29 at-bats for Sacramento. In his entire minor league career he is a .290/.374/.488 hitter.

The report from the book summarizes my current thinking about Williamson. He's a big strong guy and looks like he should hit, but he relies more on pure strength than lighting bat speed or lovely swing mechanics. He should bring much of the power forward but a high batting average and OBP should not be expected over the long haul. I do think his general athleticism is often under-rated. He's not really suited for center field, but he does a good job at either corner and can surprise you with his range.

Sabermetric projection systems give similar results: Steamer projects .248/.312/.378, ZiPS .232/.301/.360, PECOTA .247/.318/.400. The Steamer and ZiPS slash lines seem low to me; I'd anticipate something closer to PECOTA, more along the lines of .250/.320/.420. That's not exceptional production and at age 25 his window to improve isn't huge, but combined with competent corner outfield defense it should make Williamson a viable role player.