According to police, the victim, Lee Bussey, 22, was walking back to an apartment with a woman around 3 a.m. Saturday when Bussey and Lewis bumped into each other.
Police say that led to an argument and a shoving match.
A witness told police Lewis repeatedly shoved Bussey into a brick wall, causing his head to hit the wall several times. The witness told police Webb then came and the two men shoved Bussey to the ground and began punching him.
Officials said Bussey had no recollection of the incident and was bleeding from the head. He was taken to Boulder Community Hospital and received stitches.
Lewis told police they had been in Denver celebrating a friend's graduation. He and Webb then took a taxi back to Boulder and were walking home when he bumped into Bussey.
Lewis told police Bussey tried to throw a punch at Lewis but missed, so he shoved him away. He said Bussey got up and did the same thing, so he again shoved him to the ground. He said at no point did Webb ever get involved in the shoving.
Webb was Colorado's primary starter last season, throwing for 1,434 yards and eight touchdowns with eight interceptions. He is recovering after tearing his right ACL during spring practice.
Lewis, the starting left guard who announced Friday he was transferring to Nebraska, also was charged with two counts of harassment.
"Once all of the facts come to light, if Jordan is found responsible for any misconduct, he will be disciplined according to team rules," first-year Colorado coach Mike MacIntyre said in a statement. "As for Alex Lewis, as of Friday he was off of the team when he did a media interview and announced that he is transferring to Nebraska. Since he is no longer a Colorado Buffalo, it will be up to Nebraska to decide what discipline he might face."