A team has finished a game with 20-9 singles and extra-base hits 1 time since 1897, most recently Philadelphia Athletics on 1 May 1929. That is about one every 443,004 team-games.
Box score for the most recent one ↗
20-3 20-4 20-5 20-6 20-7 20-8 20-9 20-10 21-0 21-1 21-2 21-3 21-4
The whole distribution — Singles and Extra-Base Hits · All 18 shapes