This list describes the potential ways a match can end.
These are separated into results which affect ELO and ones which don't.

ELO change

Player1Win

Player 1 won via standard SC2 in game rules

Player1Crash

Player 1's bot process crashed. Player 2 is awarded the win.

Player1TimeOut

Player 1 timed out/hung. Player 2 is awarded the win.

Player2Win

Player 2 won via standard SC2 in game rules

Player2Crash

Player 2's bot process crashed. Player 1 is awarded the win.

Player2TimeOut

Player 2 timed out/hung. Player 1 is awarded the win.

Tie

SC2 declared the match a tie.

No ELO change

MatchCancelled

The match was cancelled via the website.
Currently this can result from a manual action by an admin, or an automated timeout function that the website employs to timeout long-running matches.

InitializationError

The match failed to initialize.

Player1RaceMismatch

Player 1 joined the game using an unexpected race.

Player2RaceMismatch

Player 2 joined the game using an unexpected race.

Error

There was an unexpected error with the arena client running the game.