Might be one of the least notable numbers in the years I have been following the team. Tom Ashworth maybe?
There is one notable guy at CU who wore #51. He was a multi-year starter who then went on to a long career in the NFL as a key protector for Broncos QBs, he even won a Super Bowl ring.
Answer - It was a trick question. Matt Lepsis was assigned #51 when he was a freshman at CU, he changed to #88 when he switched to TE.
That was the case for both Ashworth and Lepsis. Both guys who moved back and forth from TE to T and wore 51.
Fun note. I was Ashworth's high school back up.