Inspired by Rhu_Ru's question in Saturday's game, I decided to look it up. An hour later and I have something to check every game from 1901 through 2017. I split up the analysis into two groups, one team and combined teams, and categorized that based on length of game: fewer than nine innings, nine innings, and extra innings. The nine inning games can be either the full nine innings or nine for the visitor and eight for the home team. Fewer than nine innings required both teams to play no more than eight innings while extra innings requires both teams to play at least ten.
Nine Innings
Eight or Fewer Innings
Extra Innings
I went above ten runs scored in an inning but it gets uninteresting quickly. While searching through games with higher number of runs scored in an inning I came across two games I found interesting in some way.
First, I believe this game has the most runs scored in a single inning in modern baseball.
Second, the start of this game must have been extremely depressing for any Reds fans following the game.
What kind of Russian numbers station stuff is this!?
tl;dr: The answer is six.
If I'm reading this correctly, there's only one game in MLB history where both teams each scored 10+ runs in one of their half-innings?
EDIT - I meant 10+, I swear.
Correct, it's happened only once, since 1901.
So, the ballgame where the initial question came up should be in the chart, as the Rays had four innings of at least four runs. Fell one short of tying the two-team record though.
Once Retrosheet adds the 2018 season, I can update the tables.