Meaning 1 ►▼
In baseball their are four bases, 1st, 2nd, 3rd, and 4th. Fourth base is home; if a runner gets to 4th base he scores a run. If the runner is left on third base at the end of an inning, he does not score.
The batter scored a double and then stole third, but when the inning was over he was left on third base.
Meaning 2 ►▼
To try, but not succeed.
The young boy asked a girl he liked to the prom, but was left on third base when he found out she was going with the football captain instead.