Austin Slater has been a solid role player against left-handed pitching in his eight-year career. There is no doubt about that. However, SF Giants manager Bob Melvin made a puzzling lineup decision by inserting Slater in the lineup to start against Colorado Rockies right-handed hurler Cal Quantrill in Thursday’s 9-1 loss.

This was not the decision that led to the loss. The Rockies were the better team on Thursday. The Giants had secured the first two wins of the series and they could have gone for the sweep, but they went with a much different lineup on Thursday.

Sweeping teams is difficult. Even the worst teams will usually win one out of every three games, so the Rockies were due.

It also bears mentioning that Slater is off to a brutal start and is in the midst of a slump that extends beyond just this season. One way to get him into a groove is to put him in favorable matchups, which should be exclusively against left-handed pitching.

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That is not what Melvin went with on Thursday. Instead, he slotted the right-handed bat into the sixth slot against Quantrill. Slater has four hits in 34 at-bats in 2024. This is a very small sample and still plenty of time for him to turn it around.

For much of his career, Slater has been excellent against lefties, slashing .279/.370/.448 (128 wRC+) with an 11.0 percent walk rate, 22.6 percent strikeout rate, and a .170 ISO. He reaches base at a high clip and hits for modest power in those matchups.

On the other hand, he is relatively unplayable against righties, posting a .225/.314/.332 line (82 wRC+) with a 10.1 percent walk rate, 33.1 percent strikeout rate, and a .106 ISO. He strikes out way too much and does not offer much power upside.

Melvin details frustration after Giants fall 9-1 to Rockies

His numbers against righties are acceptable if he trades it off with above-average defense in center field, but that is just not who Slater is. He does a nice job in center field, but not to the point where a team like the Giants can overlook the below-average bat against righties.

The 31-year-old has had stretches where he has held his own against righties, but that has generally been BABIP-infused. It has never been a sustainable trend. His value comes from what he can do against southpaw pitchers even if he has not done so lately.

Bob Melvin is coming home to San Francisco as Giants manager after an  uneasy time in San Diego

In fairness to Melvin and Slater, the Giants just have not faced a lot of left-handed pitchers lately. At some point, Melvin has to find a way to get him into the lineup. The Giants will face off against two lefties over the weekend, so that feels like a good time. However, this is one game where it would have been better to shift Mike Yastrzemski to center field and let Heliot Ramos see time in right field.