Castro, one of New York's two backup catchers, said he thought the game was at 4 p.m. local time instead of 1 p.m. Castro said he was taking a shower at the team's hotel when a hotel employee knocked on his door to tell him he was late.
"I'm embarrassed," Castro said. "I was ready to come to [Petco Park] at 1 o'clock because I thought the game was at 4."
Randolph said Castro's explanation was "unacceptable." He added that Castro will be fined an undisclosed amount.
The Padres rallied for an 8-6 victory to complete a four-game sweep.