For
Competition is about results and achievement.
Against
True sportsmanship values effort and experience.
Anonymous excerpts, translated where noted.
“A trophy feels like it should be for winning?”
“The "participation trophy" was just the thing you got when you didn't win.”
“At least participation trophies mean you took place in the event/contest instead of latching on to the accomplishments of the winner.”
“Their competition, in a way, was against themselves. The point is not being better than others, but being a better version of themselves”