Marcelo Mayer’s first rehab game with the Sacramento River Cats didn’t take long to turn heads.
The new SF Giants middle infielder went deep to center field in his second at-bat Thursday night, part of a 4-3 Sacramento win over the Las Vegas Aviators. Mayer was pulled after three plate appearances, with Dario Reynoso stepping in after recently joining the River Cats from the San Jose Giants to help with extra bench coverage.
That limited workload fit the expected plan. Mayer has been working his way back from a forearm injury that sidelined him since the end of June, and Thursday marked his first rehab assignment game.
The former top prospect came to the Giants earlier this month in the deal that sent Erik Miller and outfield prospect Carlos Gutierrez to the Boston Red Sox. He had already started ramping up baseball activities at the time of the trade, but had not yet played in a rehab game.
For a Giants season that is sliding toward the finish line, Mayer offers at least one reason to keep watching. He was once considered one of the best prospects in the sport, climbing as high as No. 9 on MLB Pipeline’s list before the 2023 season. He was also the No. 4 pick in the 2021 draft.
There’s also a growing sense that Boston moved on from the 23-year-old too early. Over the past year, the Red Sox have shipped out James Tibbs III, Kyle Harrison, and Connelly Early in deals that have raised plenty of eyebrows.
Harrison’s move has already become a disaster, while the verdict on Tibbs III, Early, and Mayer is still out. At least on paper, each of those trades looked favorable for the team on the receiving end.
When Mayer is ready to join the Giants for real, there should be a path for him to play. The Luis Arráez trade, along with Matt Chapman being out for the rest of the year and Casey Schmitt also expected to miss time, has opened things up at second base and third base.
Those are both spots Mayer knows well. He has also spent plenty of time at shortstop, though that position has not produced strong defensive grades in his limited major league work. San Francisco may still give him a look there, too.
At the plate, Mayer has flashed the kind of power that keeps evaluators interested. The left-handed hitter has played in parts of the last two seasons with Boston, but he managed only a .625 OPS in 364 plate appearances.
The bigger issue has been getting on base; his .278 career on-base percentage is nowhere near starter quality. Still, he is young enough that there is room for more growth.
Across six minor league seasons, Mayer has put up an .829 OPS, including an .840 OPS at Triple-A. He has often faced older competition during his pro career, which leaves more development on the table. The Giants are hoping some of that comes together in San Francisco.
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