Buster Posey Counting on Former Phillies Prospect to Emerge as a Starter for Giants

20-year-old pitcher Ramon Marquez could bring his mind-numbing, straight change up to the Giants starting rotation by the start of the 2028 season

San Francisco Giants general manager Buster Posey speaks during a ceremony before the game. Credit: Darren Yamashita-Imagn Images | IMAGN IMAGES via Reuters Connect

The San Francisco Giants were considered one of the teams that truly fared well and improved their organization at this year's trade deadline. Mired in the midst of a muddled 2026, president of baseball operations Buster Posey made all the right moves - at least at first glance. And one of the crown jewels of his haul of talent was right-handed pitcher Ramon Marquez.

The Giants acquired the 20-year-old pitcher, along with prospect relief pitcher Marty Gair, via this year's trade deadline from the Philadelphia Phillies. In exchange, the Phillies received Luis Arraez and Caleb Kilian.

At the time of the trade, Marquez was ranked as the Phillies' No. 4 prospect. Before the transaction, he had an impressive performance, posting a 1.68 ERA with 93 strikeouts over 59 innings in 12 appearances (11 of which were as a starter) for Single-A Clearwater and Jersey Shore (High-A).

With starter's potential, Marquez must prove he has the stamina to be a part of the rotation. If he can do so, his mixed bag of pitches makes him valuable as a potential fourth or fifth starter as they finish off fixing the 'Frisco franchise. Notably, his straight changeup has been lauded by scouts and even minor league opponents as a potentially devastating out pitch... at any level.

Top prospect on top prospect crime

Ramon Marquez mows down Blue Jays #1 prospect, JoJo Parker, on 3 straight changeups

That thing is NASTY. Good morning. Good afternoon. Goodnight#SFGiants pic.twitter.com/FIqAYkue5v

— Coast to Coast Baseball (@C2Cbsbl) August 20, 2026

"Marquez quickly blossomed into one of the best pitching prospects in the Phillies system," the official report states. "The biggest question with Marquez is the considerable effort in his delivery, so he'll have to prove he can hold up under a starter's workload. His mechanics do come with good extension and a low release height, and they don't prevent him from throwing strikes with all three of his offerings. If he holds up, he could become at least a mid-rotation starter.

Giants Believe in Marquez

Giants President of Baseball Operations Buster Posey | Credit: D. Ross Cameron | IMAGN IMAGES via Reuters Connect

As for how the club itself views their pitching prospect, Posey says that they expect him to fully develop and round out as a rotation hopeful, which could come as soon as Spring Training in 2028. He'll likely end next year tossing a few innings for the Giants' Triple-A affiliate, the Sacramento River Cats, but don't expect the team to rush him to The Show. He will need time to develop, which Posey believes will end with lots of success in San Francisco.

“I’d like to specifically highlight a guy, Ramon Marquez," Posey said after making his deadline-day deals, per MLB.com writer Maria Guardado. "He was one that our scouts had flagged early on in this process, and a guy that we weren’t sure we were going to have access to. He’s somebody that we’re extremely excited to add to the system. We feel like he’s a starting pitcher that’s going to slot up in the top of our system going forward.”