New England's injury list is expanding and shows no signs of abating.

In the early going on Friday, running back LeGarrette Blount appeared to suffer a serious injury to his right knee during an interior line running drill (known as a 9-on-7). He ran into the pile and fell to the ground in a heap, where he remained on his back for several minutes with members of the medical staff, teammtaes, and even head coach Bill Belichick hovering over him at times.

However, Blount eventually was helped to his feet and managed to walk to the sideline under his own power. He spent several more minutes flexing his right leg with a medical staffer alongside him. Not long after, Blount walked slowly back to the locker room, accompanied by the medical staff.

"I didn't see it," tight end Rob Gronkowski told reporters later, "but hopefully he's all right."

Later in the session, first-round draft choice Malcom Brown sustained a left foot or ankle injury that required him to stay down on the sideline for several minutes with his shoe off. He soon put the shoe back on and remained on the field as a spectator for the rest of the practice. It did not appear that Brown's injury was too much of a cause for concern, however, as the medical staff did not treat him on the field, and the rookie defensive lineman actually spoke to reporters afterward.

"Just working and competing," he said with a smile several times in response to repeated questions.

Center Bryan Stork was also spotted in a spectator role toward the end of practice, with Josh Kline taking over for him during team period action. Stork stood with his o-line teammates, but did not have his helmet with him. It's unclear exactly why he was held out.

All this came on a day when the highest total of the summer – 21 other players on the 90-man roster – did not suit up for or take part at all in practice.

None of the players who've been on the NFI and PUP lists since camp started more than a week ago have come off, and more players continue to miss time with medical conditions. A few newcomers to that last include tight end Scott Chandler, linebacker Eric Martin, and rookie linebacker Matthew Wells. Wide receivers Julian Edelman and Aaron Dobson have now missed consecutive days, although Brian Tyms was able to come out with his helmet and take part in early warmups before leaving to do rehab and conditioning work elsewhere.

(Air) Pressuring the officials

Back Judge Tony Steratore, a 16-year NFL veteran, spoke to the media prior to practice and answered questions for 45 minutes. Steratore and a few other members of his officiating crew team have been working with the Patriots on the field and in the classroom the past couple of days. Steratore showed the media the same instructional video that was shown the the players and coaches highlighting the new rules changes and points of emphasis for the 2015 season.

In light of Tom Brady's potential suspension, many of the questions Steratore fielded from reporters focused on the league's procedures for checking air pressure in the footballs used on game days.

"Our procedure this year that we have in place is that the referee will assign two members of his crew to do the regular ball checks that we've done to approve the pressure of the balls prior to the game. Once we get on the field before the beginning of the game, we turn them over to chain of custody, for lack of a better term, and that's where the K ball (for kickers) folks and football operations will take it from there. Once we get in the game, it won't be a big concern to the officials."

Steratore confirmed that there will be random checks of the air pressure of the game balls at halftime, though not in every game this coming season. He was unsure, however, what factors will determine when the balls are checked and when they're not. That does not fall under his purview, he explained.

"Once we start to play football," he added, "that's really not a priority. We take care of that prior to the game in the preparation phase. Once we're playing football, there are plenty of challenges out there."

Steratore explained that the K balls are allowed, under the officiating crew's supervision, to be treated before use in the game

They have folks that come in an rub the balls down, get some of the factory tackiness off, and that sort of thing. It's a procedure that's been done for a really long time. Nothing terribly new about it.

Develin: 'Add to your toolbox'

Fullbacks are becoming a rare commodity these days in the pass-first NFL, yet James Develin has managed to find a nice home for himself on the Patriots roster. In fact, none other than Tom Brady has called him the best fullback in football. Not bad, especially for a former Ivy League defensive lineman who had to change positions to make it in the NFL. He had stints in the Arena Football League and now-defunct United Football League before catching on with Cincinnati, then New England, where he helped the Patriots win the Super Bowl last season.

"It is a little crazy," he reflected Friday, "but I just try to take it one day at a time. I'm just focused on this season and preparing to help this team win."

Develin insisted he doesn't ever feel "comfortable" with his spot on the roster, nor does he take his job for granted.

"I never try to look at it that way. I just have to come out here every day and prove myself, prove my worth here, and just fight as if it were my first day out here."

Being a flexible athlete, in terms of roles he can play, is what he believes has helped him get to where he is today.

"Yeah, I think versatility's the name of the game, you know," Develin explained, "because you don't want to be pigeonholed into one thing, especially as a fullback. You try to go out there and do whatever's asked of you, whether it's split out on [pass] routes or blocking in the I-formation. You just try to add to your toolbox to help the team win, and that's what I try to do every day."

Stock Watch

Buy: Jabaal Sheard – Perhaps the most consistent performer on defense thus far in camp, New England's top defensive free agent has looked better and better each day.

*Sell: *Running backs – It was a tough day for the ball carriers, with Blount going down with an injury and fumbles by James White and Eric Kettani.

Play of the Day: An amazing one-handed catch by Danny Amendola in a 1-on-1 drill against Logan Ryan. Tom Brady threw a deep ball to Amendola down the left sideline, which appeared to be too far out of his receiver's reach, but Amendola dove, extended his left arm, and corralled the ball with one arm. As he rolled over the goal line for the score, he fired the ball, from his back, into the nearby stands in celebration. A fan caught the ball and tossed in back onto the field