A team has finished a game with 21 left on base 76 times since 1897, most recently Washington Nationals on 8 May 2016. That is about one every 5,829 team-games.
Box score for the most recent one ↗
15 16 17 18 19 20 21 22 23 24 25 26 27
The whole distribution — Runners Left on Base · All 18 shapes