One I haven't seen mentioned yet that instantly came to my mind was JBJ's bases loaded, bases clearing double in Game 2 of the ALCS.
Sox are down 1-0 in the ALCS. They're down 4-2 in the game. Bottom of the third, so still early. But Gerrit Cole, Houston's Ace 1B, is on the mound. David Price, at this point still "the guy who can't get it done in the playoffs," is on the mound for the Sox, and off to a rough start.
Sox had gotten off to an early 2-0 lead. The Astros tied it on a 2 run, 2 out double, then took the lead on a 2 run, 2 out HR. This is basically a must win game for the Sox (not really) because heading back to Houston for 3 games facing an 0-2 deficit is.... not a good situation.
JD starts the inning with a K. Then it goes: Xander single, Steve Pearce double, Devers walk. Bases loaded, one out.
Kinsler strikes out. Because of course he does. (No hard feelings!)
JBJ up. Last hope of the inning. He went 1 for 17 with the bases loaded during the 2018 season, a stat mentioned at the time by the TV announcers. At this point, he was 2 for 16 in the playoffs, with 4 walks and 0 RBI. Hadn't done any damage.
Then he does this:
Slices a wall ball double that, somehow, manages to bounce up onto the left field padding and then bounce again along the top of the padding, enabling Devers to score from first. I can't recall ever seeing a ball bounce twice on that padding. The slow-mo replay is almost comical as Marwin Gonzalez waits twice for the ball bounce off into his glove, only to see it bounce a foot in front of him. Sox take the lead 5-4.
That felt like a big turning point.
Yeah, it's still way early in the game. It's still early in the series. But if JBJ makes an out there and Cole gets out of the jam, maybe doubts start to creep in. Cole retired the next 10 Red Sox he faced, with the Sox not scoring again until the Astros bullpen came in.
Instead, with one swing, the Sox took the lead in the game, ended up tying the series, and never really looked back.