Spomer was one of several Bulldogs who spent the summer at NFL training camps, but he was the only rookie to make an initial 53-man roster.
The center received significant opportunities during the preseason and moved up the depth chart after injuries affected the Chargers' starting offensive line. His performance was enough to secure a roster spot.
Former Fresno State coach Matt Entz praised Spomer's work ethic and football intelligence.
"You're going to get a guy that's going to show up every day and work hard. He's a very cerebral football player. He's going to pick it up really quick and I'm sure that was part of the reason why he was able to land on the 53," Entz said.
Spomer said the experience of training camp helped him develop both on and off the field.
"I definitely grew as a player and a person... just around the guys, it was a veteran group. A lot of very good people in there and also good coaches, so definitely grew a lot," Spomer said.
Spomer is listed as the backup center behind fellow rookie Jake Slaughter, the Chargers' second-round draft pick.
The Chargers open their season against the Cardinals on September 13.