The death of a Plano high school football coach who collapsed Monday evening was heat-related, according to a preliminary autopsy report.
Wade McLain, 55, collapsed after the first day of practice this season. He died of heat exposure combined with a heart condition, the Collin County Medical Examiner's office said.
As the Prestonwood Christian Academy team was running off the field to take an extended break from the triple-digit temperatures, McLain lost consciousness.
"He showed no signs of having an issue on the field whatsoever," said the Rev. Dr. Jack Graham, who spent time at the team's first practice. "I was watching him. He was just working hard and having a great time doing it -- smiling, laughing, like he always was."
Monday was the first day Texas high school football teams were allowed to hold official practice. Temperatures reached a high of 107 degrees in North Texas on Monday.
The team's trainers tried to revive McLain. He was rushed to a nearby hospital, where he was pronounced dead.
Prestonwood Christian Academy announced McLain's death on its website Monday night.
"We are deeply saddened to let you know that this afternoon, assistant varsity football coach Wade McLain died unexpectedly following the team's regular practice," the school said in a statement on its website. "Please be in prayer for Coach McLain's wife, Becky, and their five children. We are deeply saddened by the loss of Coach McLain yet are thankful in knowing he is in the presence of Jesus."
Two of McLain's sons were present at the practice. One of his older sons was at the field visiting his father and another son, Christian, plays football for the Lions.
Graham said the team took plenty of water breaks and got adequate rest but the school plans to evaluate how it operates its football program.
"Heat is always a major concern, so we will do what we have been doing, which is to take extreme precautions, provide breaks and water and air-conditioning and be sure our students are safe," Graham said.
Hundreds of people gathered at the school affiliated with Prestonwood Baptist Church for a private prayer vigil at about 8:30 p.m. Monday.
McLain helped coach the Prestonwood football team to back-to-back state championships in 2009 and 2010.
His colleagues said he also taught history and coached baseball at Prestonwood.
Friends described him as a strong Christian who influenced thousands of young lives over the years as a football coach.
McLain's neighbor, Judy McBroom, said he had a gentle heart and offered to help her when she hit hard times.
"He came over and talked to me and offered his help to have his boys mow my yard... They are just helpful, nice people," she said. "I'm just crushed. It's just such a shock. Why do the good people have to be taken from us?"
A memorial service at Prestonwood Baptist Church is planned for late this week.
"Everything that we believe is that death is not the end, and Wade, of course, was a strong believer and follower of Christ, and he was doing what he loved to do, which was to coach football," Graham said.
NBC DFW's Ellen Goldberg contributed to this report.