The youth soccer player -- who killed a referee, with a single punch, last April -- has pleaded guilty to Homicide by Assault.

In exchange for the plea, he will remain in juvenile jurisdiction.

That means he can serve no longer than just over three years, until he reaches his 21st birthday.

He will also avoid an adult legal record.

The 17-year-old boy's defense attorney says his client has no criminal record, and made one horrible mistake.

The youth -- who is not being identified -- apologized to his victim's family as he entered his plea, Monday morning.