Complex sentence: Injuries kept Citation from racing in 1949 but he came back to race in 1950 and won the Golden Gate Mile Handicap but lost several other races in what for him was a mediocre campaign.
Split into simpler sentences: Injuries kept Citation from racing in 1949 but he came back to race in 1950 and won the Golden Gate Mile Handicap. However, he lost several other races in what was for him a mediocre campaign.