baseball player vs participant

baseball player and participant both are nouns.

Word	Noun	Adjective	Verb	Adverb
baseball player	Yes	No	No	No
participant	Yes	No	No	No

As nouns, participant is a hypernym of baseball player; that is, participant is a word with a broader meaning than baseball player:

Other hypernyms of baseball player include athlete, jock, player.

baseball player (noun)	participant (noun)
an athlete who plays baseball	someone who takes part in an activity
	a person who participates in or is skilled at some game