This is a depth move, one that was probably pushed to a higher priority once Melvin Ingram tore his ACL, but Keiser probably shouldn't be considered as a possible starter in Ingram's absence.
Thomas Keiser is 24 years old and played college football for Stanford University. He went undrafted in 2011 and spent the first half of the season on Carolina's practice squad. In the finals 8 games of the season, he picked up 4 sacks in 205 snaps. In 2012, he racked up one-half of one sack in 106 snaps before being put on Injured-Reserve with a left elbow injury.
Keiser played mostly Defensive End for the Carolina Panthers, but he was more of a 3-4 OLB at Stanford. Also, he should be somewhat familiar with the defense since Ron Rivera had an influence on what John Pagano does in San Diego.
This could be a sleeper pickup, someone that Tom Telesco has liked for years and finally thinks he has the right fit for him, but even if Keiser never starts a game as a Charger this is a solid depth move.