1977 triple crown winner crossword clue

 Sure, here is a cryptic crossword clue for the 1977 Triple Crown winner:

Slew the competition (11): SEATTLE SLEW

The wordplay clue in this clue is the word "slew." Slew can mean to kill or destroy something. In this clue, the word "slew" is being used as a homophone for the name of the horse, Seattle Slew. Seattle Slew was the 1977 Triple Crown winner, and he is considered one of the greatest racehorses of all time.

I hope this helps!