Bills' first practice: What to expect

PITTSFORD, N.Y. -- The Buffalo Bills will become the first team to open training camp Sunday, holding a practice at St. John Fisher College at 6 p.m. ET.

Per NFL rules, the team isn't allowed to be in full pads until its third practice (on Tuesday). That means players will be in "shells," or lighter shoulder pads, and there will be more of a focus on the passing game.

Don't expect fans to complain about that. Tickets are sold out for Sunday night's practice, which will be the first time the public can see EJ Manuel and first-round pick Sammy Watkins together on the field.

That will be the main attraction, but there will be other areas to watch. Here's what else you can expect:

Players not participating: Barring any late changes, defensive tackle Marcell Dareus isn't expected to practice Sunday. He remains on the active/non-football injury list along with linebacker Kiko Alonso, who is out for the season and isn't with the team in Pittsford. In addition, starting left tackle Cordy Glenn and defensive tackle Alan Branch both remain on the active/non-football illness list and aren't likely to practice Sunday night. Rookie linebacker Randell Johnson should also be sidelined, as he remains on the active/physically unable to perform list.

Changes on O-line: With Glenn out, seventh-round pick Seantrel Henderson is expected to take first-team reps at left tackle. Henderson had an up-and-down minicamp in that role and could be going against defensive end Mario Williams in 11-on-11 drills. We'll keep a close eye on that battle. There are also questions on the right side of the line. Does Chris Hairston take first-team reps at right guard over Kraig Urbik? Does Erik Pears or Cyrus Kouandjio get the first crack at right tackle? Sunday's practice should give a good indication of how the coaching staff views those four players fitting in.

Rookie replacement for Alonso: On Friday, general manager Doug Whaley mentioned third-round pick Preston Brown and third-year linebacker Nigel Bradham as possible replacements for Alonso. We expect Brown to get the initial reps with the first team, but it wouldn't surprise if defensive coordinator Jim Schwartz shifts some of his pieces around as camp unfolds. If fans want to get a feel for the new-look Bills defense, linebacker is a good place to start. Between Brown, Brandon Spikes and Keith Rivers, it will be an entirely different group.