The Giants selected Seth Lonsway to their major league roster on August 29, 2026, putting the left-hander in position to make his Major League debut whenever he gets into a game. The move came before a doubleheader with the Diamondbacks, a day when the Giants were likely to need extra arms.
Matt Wilkinson started Game 1 after being called up from Triple-A Sacramento and served as the official 27th man for the twin bill, while the Giants also optioned Spencer Bivens to Sacramento. That left room for Lonsway without any further roster move because the Giants already had an open spot on the 40-man roster. In practice, the selection meant the club could use him right away if the doubleheader forced a longer look at the pitching staff.
Lonsway, 27, was a sixth-round pick by the Giants in the 2021 draft out of Ohio State, and his climb back to the roster has been built on a ground-ball profile more than strikeout power. In 2026, he produced a 57.7% groundball rate over 75 2/3 combined innings at the Double-A and Triple-A levels, rarely leaned on a traditional fastball and worked with a 90.4mph sinker as his primary pitch. He also mixed in a cutter, changeup and slider.
His Triple-A line explains why the Giants may not view him as a clean starter-only answer. Lonsway had a 5.37 ERA over 114 career Triple-A innings and started 25 of his 29 games there, while at Double-A he posted a 3.02 ERA over 128 1/3 innings and started 24 of 26 games for the Richmond affiliate. The hitter-friendly setting of the Pacific Coast League may have worked against him in Triple-A, but the broader shape of his profile still points to a pitcher whose value comes from getting the ball on the ground.
The Giants said Lonsway could be used as a starter, but long relief is the likelier path if he is going to stay on the major league roster. That is the part of the move that matters most beyond Friday: not just whether he gets his debut, but whether he does enough in the kind of compressed day a doubleheader creates to remain with the club after the weekend.
For Lonsway, the call answered the one question that matters first. He was no longer waiting for the first big league appearance; he was on the roster for it. What comes next is narrower and more unforgiving — whether the Giants turn to him that day, and whether the chance lasts beyond a single weekend.
