Nebraska coach Scott Frost said Thursday that potential tampering by Oregon State led the Cornhuskers to list the Pac-12 school among institutions not permitted to contact running back Greg Bell about a potential transfer.

Bell, a top-rated junior college prospect signed by Frost last December, started the first three games for the Cornhuskers this season. He then requested a scholarship release in the week after he lost the top position on Sept. 29 against Purdue.

Nebraska granted his release but restricted Bell from talking with fellow Big Ten members, non-conference opponents of Nebraska over the next three years and Oregon State.

Three Nebraska players recently transferred to OSU, including former four-star prospects Tristan Gebbia, a quarterback, and receiver Tyjon Lindsey. Both players were recruited to Nebraska by former coach Mike Riley, who now works as an analyst at Oregon State under Jonathan Smith.

Ex-Nebraska assistant Trent Bray is also on staff at OSU, as are three former members of Nebraska football administrative staff.

"There's no doubt in my mind that those kids were probably in touch with some people that they formerly knew that were here," Frost said of Gebbia, Lindsey and linebacker Avery Roberts.

Through a spokesperson, Oregon State said the school would have no comment.

This isn't the first time Oregon State has been accused of tampering. In May, Hawaii football coach Nick Rolovich called out Oregon State on social media for sending recruiting materials to his current players. Oregon State said the mailings were unintentional and that it was committed to following NCAA rules. Three Oregon State assistants had worked at Hawaii in recent years.

NCAA rules prohibit contact about a potential transfer from an outside school with currently enrolled players.

Frost said "it's hard for me to criticize [Oregon State] without being hypocritical," noting that he spoke with his former UCF player McKenzie Milton just this week to wish the quarterback well on his birthday.

"But at the same time," Frost said, "if someone is contacting our kids while they're still our kids, then I'm not going to be a fan of that."

Bell said last week that he was confident he would find a destination and thanked Frost in a statement released on Twitter.

Changes to the transfer system that go into effect on Monday will invalidate instructions like those issued last week by Nebraska. The new rule, a step aimed to bring reform to transfer process, allows a student-athlete to notify his or her school of a desired transfer.

The school then is allowed two days to place the student-athlete into a database of transfers. Restrictions on permission-to-contact for transferring players will no longer exist.

In the case of Bell, he could again notify Nebraska of his intention to transfer next week and would not be subject to any restrictions.

Another rule change that goes into effect this year will increase the potential penalty for tampering.