Other forms: blockings
When you obstruct someone from seeing or doing something, that's blocking. In most sports, blocking your opponent is a huge part of playing the game.
Blocking the player who's trying to make a basket is one kind of blocking. There's also blocking a street for the neighborhood block party, or blocking your ex-friend on social media. In each case, you're cutting off access in some way. In theater, the word takes on a different meaning, "the staging of actors." This use stems from the 19th-century theater, when directors would frequently use wooden blocks to plan out the actors' positions on a miniature stage.