SAN DIEGO -- The San Diego Chargers cut 21 players Saturday, trimming their roster to the NFL-mandated 53 players. However, these initial rosters are written in pencil. The Chargers can claim players from other rosters off the waiver wire starting Sunday at noon ET. San Diego has the No. 3 claim priority.

Nose tackle Damion Square was placed on the reserved/suspended list. Square will miss the first four games of the regular season for violating the league’s substance abuse policy. Square is eligible to return to San Diego’s active roster on Oct. 3 following the team’s Oct. 2 game against the New Orleans Saints.

First-round pick Joey Bosa remains on the exempt list. Square and Bosa do not count toward the team’s 53-man roster.

Here’s a closer look at the final cuts:

Most significant move: The Chargers decided to keep four running backs, waiving undrafted rookie fullback Chris Swain. The Navy officer offers versatility with his ability to play fullback, tailback and special teams. Swain scored a touchdown in San Diego’s final preseason game against the San Francisco 49ers on the team’s annual "Salute to the Military" night. However, Swain is still learning how to play fullback in a pro-style offense and likely will return to the Chargers on the practice squad if he clears waivers. Part of fulfilling his military obligation as a Navy reserve officer, Swain must perform two duty days a month with the Navy at nearby Coronado Island if he rejoins the team.

Most significant non-move: Hard-hitting safety Dexter McCoil remained with the organization on the active roster. And the former CFL standout earned it: He led the team in tackles during the preseason with 23 solo stops and also forced a fumble. McCoil also finished with three special-teams tackles and should play on certain packages for the Chargers during the regular season.

Chargers move on from Mike Bercovici: The undrafted Arizona State quarterback quickly picked up offensive coordinator Ken Whisenhunt’s system and showed progress during training camp, but that did not translate to games. He played in all four preseason games and completed 24 of 44 passes for 296 yards, with one touchdown and five interceptions. He was sacked four times and had a 43.6 passer rating. If he clears waivers, Bercovici should return to San Diego on the team’s practice squad.

Spencer Pulley makes the cut: The Chargers continued the team’s streak of having at least one undrafted rookie make the 53-man roster during Mike McCoy’s tenure. Pulley, an interior offensive lineman from Vanderbilt, showed an ability to quickly pick up the offense and he can play both guard and center.

Chargers moves: Released WR Rasheed Bailey (injured), QB Mike Bercovici, T Brett Boyko, CB Richard Crawford, LB Ben Gardner, RB Gus Johnson, DT Kamal Johnson, G Marcel Jones, DT Chuka Ndulue, S Adrian McDonald, ILB Shaq Petteway (injured), WR-KR DeAndre Reaves, ILB James Ross, CB Larry Scott, TE Tim Semisch, FB Chris Swain, G Vi Teofilo, LB James Vaughters, TE Matt Weiser, WR Dom Williams, CB Trevor Williams.