The Reliability score indicates how often a player drops out of a game; whether that's because they lose connection or leave the game on purpose (the app can't tell which is which, it just knows the player is gone).

Higher deductions of Reliability happen if:

a) the player who drops out is behind in points

b) the player comes back to play after computer takeover (leaves the app, waits a while, then goes back and continues to play against the AI)

Don't worry if your Reliability score isn't 100%! Game interruptions happen occasionally and may be the result of unrelated connection problems or software error.