Bob,
Rosen also held the AL record for HRs by a rookie when he hit 37 in 1950. Mark McGwire broke the record with 49 in 1987.
After his tremendous season in 1953, he started 1954 on fire again and after 38 games was leading the league in HRs with13, RBI with 49, and second in batting at .367.
He then hurt his back, missed several weeks and was never the same hitter again. He retired after two more seasons at age 32. A largely unknown star to most people today.