What has to happen to be awarded a single base or two bases

[tucktheump]

If it is the first play by an infielder, then its two bases from the time of the pitch.

Remember, in a double play situation, the first play has already been made, so it's two bases from the time of the throw. 99.9% of the time the batter runner has not attained 1B at the time of the throw, so he is awarded 1B & 2B.

ANOTHER DOOZY:
A fair batted ball that is intentionally touched with any equipment detached from the fielder...the award is three bases. Example: pitcher throws his glove and touches a ball that is hit past him. Batter runner is awarded 3rd.