Answer:
The necessities of baseball are a field to play on, with 4 bases and a pitcher's mound or rubber. At least one bat to be shared must be present. There must be at least 18 players for a full 9 vs. 9 game. There also must be at least 9 mitts to be shared for the team on defense. Other extras like helmets, batting gloves, and umpires make the game easier and safer but aren't pure necessities.