Major League catcher Danny Jansen goes into the record books permanently today as the first MLB player to play for both sides in a single game. He started the game as a Toronto Blue Jay, and will finish it as member of the Boston Red Sox. The two teams went against each other on June 26th, but the game was called for rain. Then the Red Sox traded three minor-leaguers for Jansen on the 27th. The postponed game resumes today at the exact point it was called off in June. That was, strangely, as Jansen was at bat, with one strike. Today, he will be behind the plate catching. The Jays are expected to use a pinch-hitter in his place. The lineup for both teams has changed considerably since June, but Jansen is the only one on both teams' rosters. It's the first time this has happened in Major League Baseball's regular season, and will be a trivia question from now on.
Also, because this game will go down in the record books as occurring on June 26th, three players might be listed as having played an MLB game weeks before their MLB debut. If Joey Loperfido gets in the game, he will be recorded as having played two games for different teams on June 26th, since he played for the Astros against the Rockies on that date. And if you like weird sports stats like that, there are more in the comments at Metafilter.