The Patriots opened their three-day mandatory mini-camp in Foxborough under mostly cloudy skies with 77 players in attendance. While there were some players who returned after sitting out the OTA session a couple weeks ago, most notably cornerback Malcolm Butler and long snapper Joe Cardona, there were also some high-profile players who remained sidelined.

Rob Gronkowski topped that list but he was not alone. Julian Edelman, Danny Amendola, Dion Lewis, Logan Ryan and Duron Harmon all joined him among those out of uniform.

Those in attendance were put through the paces during a choppy practice that saw more than its share of incomplete passes. The coverage was particularly tight in many occasions and forced all three quarterbacks to hold onto the ball longer than expected frequently.

Obviously, evaluations during mini-camp are somewhat useless as Bill Belichick often explains that the workouts are strictly about teaching. So drawing any conclusions about the crispness of the passing game in June doesn't seem like a wise thing to do.

Moving on, here are one man's blogservations from Day 1 of mini-camp:

-In addition to the players already mentioned, there were several others not seen. LeGarrette Blount, Nate Ebner (rugby), Tre' Jackson (knee), Josh Kline, Shaq Mason, Sebastian Vollmer and Nate Solder (biceps) also were not in uniform.

Butler spoke to the media after practice and was rather vague in explaining his prior absence. First he indicated he was absent due to "off-field issues" and "miscommunication." He then answered a follow-up by saying it was "family-related." When asked about his contract he said refused to discuss the details and said only that he would continue to work hard and focus on controlling what he could control.

There was some good news on the absentee front, however. Butler, Cardona, Alan Branch and Frank Kearse, all of whom missed the OTA session two weeks ago, were on the field and in uniform.

-Cardona's return, in addition to various reports, seems to point toward his return for a second season in New England. There was some concern earlier in the offseason that he could miss the season while continuing to fulfill his commitments to the Navy, but subsequent updates have painted a rosier picture. After practice he said that he would be returning to Bath, Maine, as part of his Naval duties following the completion of mini-camp.

-Speaking of Navy, Cardona was surprised to see members of his former coaching staff on hand for the workout. Head coach Ken Niumatalolo and several of his assistants were on the field and Belichick spent several minutes chatting with Niumatalolo.

-Former wide receiver and Patriots Hall of Famer Troy Brown was on the field and worked with wide receivers. Former running back Sammy Morris worked with the backs during OTAs earlier in the spring.

-There were some additional markings on the near field toward the end zone closest to the Revolution practice fields. There was a triangle with the sides starting at the 10-yard line coming to a point at the 18. It's unclear why the triangle was there but based on its dimensions it's possible the markings were used to help the running backs find the proper depth behind the line. The sides of the triangle stem from points where the tackles would normally line up, similar to the offensive line spacers the Patriots have used frequently over the years.

-Not sure if this qualifies as reading too much into a situation but it was interesting to see fullback James Develin working with the tight ends during drills while fullback Joey Iosefa remained with the running backs. Michael Williams remains in his No. 85 jersey and continues to work at tight end. In fact he made a nice catch deep down the seam late in the practice.

-Tackles Marcus Cannon, Keavon Milton, Cameron Fleming and LaAdrian Waddle all worked with the tight ends during some positional drills early in practice. Obviously backup tackles often are used as extra tight ends and this was an opportunity to get work in in that regard.

-Robert Kraft made an appearance on the field about midway through the practice. The owner spent some time chatting with tight end Martellus Bennett on the sidelines during a special teams drill.

-Offensive coordinator Josh McDaniels was quite animated during the two-hour session. He was shouting instructions early and often, many times in an animated fashion. Most of his comments seemed to be directed toward the running backs and tight ends running routes while working with the quarterbacks.

-The offensive line had some changes on Monday with Bryan Stork taking over at center for David Andrews after the two flipped roles two weeks ago at OTAs. Stork worked with a group that included Waddle at left tackle, Joe Thuney at left guard, Jonathan Cooper at right guard and Cannon at right tackle. The next group had Andrews and Ted Karras alternating at center and left guard with Fleming (LT), Chris Barker (RG) and Milton (RT).

-While Butler returned to action he did not enjoy a great day in coverage. He allowed Aaron Dobson to get behind him on a deep ball and then surrendered another long ball to Chris Harper on the next play. Harper got past both Butler and Devin McCourty and made a nice adjustment to split the two.

-Speaking of Dobson, he made a terrific one-handed catch for a touchdown after beating Darryl Roberts and E.J. Biggers on a deep ball. Biggers, incidentally, appeared to take plenty of reps at safety and working in the slot. At 6-0, 185-pounds he is a bit bigger than most slot corners.

-Rookie receivers Devin Lucien and Malcolm Mitchell had some trouble holding onto the ball during Monday's practice. Lucien in particular struggled, and then appeared to injure his right foot and sat out the remainder of the practice. Mitchell failed to secure a couple of catchable passes, and he appeared to be rather nonchalant after catching a few balls later in practice. Mitchell has definite ability to separate as he was able to shake free deep down the sideline on a couple of occasions but each time was unable to catch the ball and keep his feet in bounds. On one he lost control of the ball out of bounds after it appeared he only had one foot in bounds anyway. Both are rookies trying to learn their way so it's far too early to make any judgements but Monday was not a great day for the pass-catching rookies.

-Rob Ninkovich was quite active throughout the practice, including on the first pass of the day in full team action. Tom Brady tried to complete a short pass but a dropping Ninkovich caught him by surprise and picked off the pass. Ninkovich spent a lot of time working as a true off-the-line linebacker, which is not a role he's done much of in recent seasons.

-Rookie quarterback Jacoby Brissett showed nice awareness while making an adjustment before a play late in practice. Working in a two-minute drill, Brissett noticed that his two wideouts on the left side were both aligned on the line of scrimmage and therefore in danger of drawing a penalty. Brissett pointed the error out immediately and tried to correct it.

-Keshawn Martin enjoyed a strong day catching the ball all over the field. Martin darted through the Patriots secondary on numerous occasions, mostly catching balls over the middle, and was quite productive. Martin's lone miscue came when he mishandled a punt.

-Rookies Cyrus Jones and V'Angelo Bentley joined Martin returning punts. Ryan Allen was outstanding, booming several long and high punts, forcing the returners to scramble to receive them. Allen also did a nice job of knocking some punts out of bounds inside the 5 during some individual drills prior to the return work.

-Veteran wideout Nate Washington appeared to struggle getting on the same page as Brady early in practice The two tried to hook up on a couple of occasions but the timing wasn't right and the passes fell incomplete. However, later on Washington and Brady connected a few times and the receiver appeared more comfortable as the day went on.

-Midway through the session Belichick called for 7-on-7 drills to be run simultaneously on the far field. Starting at or around midfield the two offenses went to working in opposite directions. The execution during this period was not great as several passes found their way to the turf on each side. Also, the quarterbacks often held onto the ball for long periods of time while searching to targets, an indication that the coverage was solid. The secondary included Jones, Butler, Justin Coleman, McCourty and Patrick Chung during one of those periods.

-Geneo Grissom was forced to run a lap after jumping offside on one rep.

-Rookie linebacker C.J. Johnson spent time running sprints across the field under the watchful eye of trainer Jim Whalen.

-With the punt unit getting some work on the far field, Brady and Bennett spent time on some red zone throws on the opposite side. Bennett looks like a potent forced in that area, making some one-handed grabs look quite easy. At the same time Brissett was seen working with Dobson, Mitchell, Harper and Washington in the middle of the field. When those drills were finished, Brissett joined Brady and eventually tossed a pass in his direction as the GOAT made the catch while tapping his feet in bound under the goal posts.

-The Patriots will continue their mandatory mini-camp on Tuesday in Foxborough. The practice will once again be open to the media but closed to the public.