A 17-year-old soccer player in Utah pleaded guilty Monday to homicide by assault in the death of referee Ricardo Portillo, an official said.A judge ordered the teenager, who has not been named publicly, to keep a picture of Portillo in his cell phone for the remainder of his time in juvenile jail.The judge recommended a sentence of three years, said Salt Lake County District Attorney Sim Gill.Is teen violence out of control?In addition, the judge ordered the teen to write weekly letters to Portillo's family members, telling them what steps he is taking to return to normal life. On April 27, Portillo, 46, was refereeing a game of Fut International, a Hispanic soccer league for children between ages 5 and 17, in the Salt Lake City suburb of Taylorsville.He cited a player for an infraction and issued him a cautionary "yellow card." A second infraction would result in the player's ejection from the game.Slain referee risked violence for 'his passion' The 17-year-old player, police said, turned around and punched Portillo in the face.At first, authorities thought Portillo suffered only minor injuries. But at the hospital, doctors discovered serious internal head injuries. For seven days he remained in critical condition. He later died from his injuries.Portillo had three daughters and three grandchildren, who live in Mexico. He moved to the United States 16 years ago."I just need time to heal. It's a lot of pain that this kid caused my whole family, especially my sisters and I," Johana Portillo, his daughter, told CNN in May."I will forgive this kid because it's only in God's hands. ... But right now, it's too soon for me to forgive." Soccer violence: referees under siege