How do you spectate a game?

Games Halo 5: Guardians
1

I believe there is an achievement for this.

2

Wondering the same thing my self . any news?

3

spectate a friend while they play matchmaking?

4

Choose the option to join a friend in a custom game from the fireteam menu, and it should give you an option to spectate it.

5

Go to the list that shows “Fireteam - Friends - Recent”

Choose a recent player (or friend if they’re playing), and when you click their name you will be given multiple options. One of which is “Spectate” if they are in an active game.