WR Anthony Armstrong injured the AC joint in his right shoulder after crashing to the ground following a leaping attempt to catch a pass. Armstrong was examined by trainers on the field and will undergo an X-ray, though coach Mike Shanahan said he thought he’d be okay. S DeJon Gomes will miss the next two days with a sore shoulder. RT Jammal Brown will begin rehabilitating his hips at Redskins Park on Thursday. Coach Mike Shanahan said Brown is in better shape than in the past, so he’s hopeful that a combination of anti-inflammatories, rest and rehab will help.

RG3 Update: Robert Griffin III continues to hold onto the ball too long, a sign he’s still learning the offense and doesn’t want to force passes. He’s also learning to throw under duress, although he’s impressed teammates with his ability to adjust under pressure. Griffin did make a few bad throws, one of which was intercepted by CB Kevin Barnes. The veteran fooled Griffin with his coverage, peeling off another defender to jump the route. Griffin also threw high and wide to Brandon Banks on the play, leading to the pick.

Welcome back: S Tanard Jackson practiced for the first time in training camp, after sitting out the first six days with a calf injury. Jackson worked with the second string defense and allowed a big pass play on a deep post off a bootleg. But he needed to get more help from CB Kevin Barnes on the play. Barnes allowed WR Brandon Banks too clean a break off the line.

Rusty return: New OT Jordan Black got his first work with the Redskins second offensive line and played like a guy who had been out of football for a year. Black needs time to get his football legs back not to mention readjusting to the speed of NFL pass rushers.  That much was clear as LB Chris Wilson sped past him to the outside on consecutive plays. The Redskins signed Black earlier this week.

The replacements: Replacement officials worked Thursday’s practice and drew the ire of the defense after one disputed catch by TE Chris Cooley. The veteran TE made a diving grab, beating rookie LB Keenan Robinson -- right in front of the defense’s sideline. That, of course, prompted a number of defenders to bemoan the lockout by the officials.

Follow John Keim on Twitter @CBSSportsNFLWAS or @John_Keim.