The 22-year-old Acho will compete for a backup inside-linebacker job, which requires significant special-teams duty. Jamar Chaney and Casey Matthews are currently the backups to likely starters DeMeco Ryans and Mychal Kendricks. The Eagles are expected to switch to some version of a 3-4 scheme.
Acho (6-foot-1 and 240 pounds) ran a 4.73-second 40-yard dash at last year's NFL combine. He earned first-team all-Big 12 honors as a senior and finished his college career with 280 tackles, eight sacks, seven forced fumbles, three fumble recoveries, and two interceptions.
Eagles defensive coordinator Bill Davis was Acho's position coach in Cleveland, and Eagles offensive coordinator Pat Shurmur drafted the linebacker when he was the Browns' head coach.
Lewis, 22, was selected out of Pittsburgh in the fifth round of the 2011 draft. He returned kicks most of his rookie season but averaged only 21.6 yards a return. After rushing 23 times for 102 yards in his first season, Lewis carried the ball only 13 times for 69 yards as he fell behind Brown on the depth chart.
He did run for a 17-yard score against Washington in the second-to-last game of last season.
The running game should be a strength for the Eagles. McCoy and Brown will likely get the bulk of the carries, but Kelly praised Polk last month during the NFL owners meetings. Kelly saw plenty of Polk in college when Oregon faced Washington.
Polk, who played exclusively on special teams, was sidelined by a foot injury for most of his rookie season.
Four released. Kelly continued to fiddle with the Eagles roster when he released linebackers Ryan Rau and Marcus Dowtin, wide receiver Ron Johnson, and cornerback Chris Hawkins on Thursday.
Only Rau played last season for the Eagles. Dowtin finished the season on the practice squad. Johnson suffered a broken ankle during training camp and spent all of 2012 on injured reserve. Hawkins was signed early this offseason.
All four were considered long shots to make the 53-man roster.
Contact Jeff McLane at firstname.lastname@example.org. Follow on Twitter @Jeff_McLane.