"Rushel and I met on Tuesday morning and he informed me of his final decision to transfer," coach Paul Chryst said in a statement. "I wish him only the best moving forward. Out of respect for Rushel, his family and his privacy, this will be my final comment on the matter."
Expectations were high for Shell heading into this season, as he was the leading candidate to replace Ray Graham, one of the most productive running backs in school history.
As a true freshman, Shell was the team's second-leading rusher with 641 yards and 4 touchdowns on 141 carries for a 4.5-yard average.
Last week, Pittsburgh announced that Shell was taking some time away from football to "work through some challenges." His decision to transfer leaves the position lacking experience.
The bulk of the carries will now go to junior Isaac Bennett, sophomore Malcolm Crockett and senior Desmond Brown. Bennett has been the most productive with 378 career yards and 5 touchdowns on 87 carries (4.3 avg.). Crockett had 50 yards on 12 carries (4.2 avg.) as a redshirt freshman last season, and Brown's contributions came on special teams.
Chryst said Bennett and Crockett both have their strengths.
"They're different," he said, according to the team's practice report. "They both have similarities. They both run hard. They like the game. Malcolm can continue to learn to tempo his runs. Sometimes he has just one speed. They seem to have different styles.
"All that matters is playing their strengths," Chryst said. "There are guys who are strong in a lot of areas. You can play to each player's strength."
Crockett said he has been waiting for this opportunity.
"When a man goes down, the next one has to step up," he said, according to the team's practice report. "It's something I've been preparing for. I know my time will come. It's here, so every rep, every second I'm just going hard to the fullest. Eventually, I'm going to try to start."