Chantilly RB Ross Simms (1) dives into the end zone to score a touchdown against Stone Bridge earlier this season. (Richard A. Lipski/for The Washington Post)

When Ross Simms walked off the football field after a morning preseason practice at Chantilly in August 2011, he felt like a player on the verge of a breakout junior season at tailback.

But as the afternoon sun gave way to dusk, the 16-year-old suddenly felt on the brink of a breakdown. For five straight hours, Simms had been hovering over the toilet, throwing up every 30 minutes.

After being rushed to the hospital, doctors immediately examined Simms’s kidneys. Not only was he severely dehydrated but tests also showed that Simms was losing a great deal of muscle protein with every trip to the bathroom. At this rate, his kidneys were deteriorating fast, making a transplant one of the few viable options.

“I couldn’t stop throwing up, even after I got to the hospital,” recalled Simms, now a senior running back in the midst of a strong season that appeared unlikely last fall. “The doctors said that if I hadn’t come in that night, I might have died because my kidneys were so damaged.”

How Simms, who up until then was a healthy teenager with a year of varsity football under his belt, had reached this point was initially anybody’s guess. Even after his kidneys began to stabilize, that same question remained unanswered for nearly a month.

Chantilly senior Ross Simms is back on the football field after suffering from a mysterious blood condition. (Brandon Parker/The Washington Post)

Simms was finally diagnosed with TTP, a blood disorder that causes blood clots, as well as rhabdomyolysis, which deteriorates muscles and releases the damaged cells into the bloodstream. Simms would have to spend another month in the hospital undergoing blood transfusions to cleanse his bloodstream.

But the first thing on his agenda was taking a walk around the hospital. Most of his strength, along with about 30 pounds, had been zapped since entering the hospital, forcing him to pass the time playing football on the Xbox that his mother had brought to his room. Still, once he placed his feet on the cool hospital floor, he figured he could circle his room at least once.

He only made it five steps.

“That was probably my lowest point,” Simms said. “My mind-set was that I was going to play football again, so when I couldn’t really walk, I began to think that maybe I never would play.”

Tears welled up in Simms’s eyes as his dad pushed him back to his bed in a wheelchair.

He vowed to improve. One week before leaving the hospital, Simms climbed the stairs in the hospital cafeteria for the first time.

Simms’s return to normalcy wasn’t always a smooth one, though. During his first few weeks back at school, he had to use the elevator to get from class to class. And even as his energy was restored, his training was limited by the tube temporarily inserted into his chest for weekly blood cleansings.

Yet through his determination — and a few admitted maneuvers around the doctor’s orders to take it slow — Simms worked his body back into shape for Chantilly’s Nov. 11 playoff game against West Potomac. And though he played sparingly, the joy of being back on the field overrode any jitters Simms may have had.

“If anything, I was excited to hit somebody,” Simms said with a laugh. “My mind-set from when I got out of the hospital was to keep pushing to the limit.”

That attitude continued through the offseason, as he committed to not only working harder but smarter. Before and after each practice, Simms chugged fluids. He was careful not to overexert himself.

On Aug. 30, a little over a year after Simms entered the hospital, the senior marked his second return to action by scoring three touchdowns in a victory against W.T. Woodson. Through six games, Simms is second on the team in rushing yards (500) and first in touchdowns (seven).

Outside of some surgical scars and periodic blood tests, there are few signs of Simms’s near-death experience. If anything, Simms is reminded daily of how fortunate he is not only to be alive but to have a second chance at football.