Efraín's mother died when he was a little boy, and Don Mon remarried a few years after, fathering a total of twelve children. Since the family's economic situation was precarious, Efraín had to support and look after his younger brothers by taking various odd jobs. The one that he was most successful at, besides music, was as shortstop for the Indios de Mayagüez, the local winter league baseball team, for which he had been the bat boy at an earlier age. He played with them between 1943 and 1945. To this date, he still holds the league record for most triples in a game (three) and most consecutive doubles in a double-header (five).