1. ONE DAY DOWN, 257 TO GO: Head coach Ron Rivera liked the excitement and energy surrounding the Panthers' first of 10 organized team activities over the next three weeks, but he didn't like everything about Tuesday's session.

"I was pleased with what I saw for the most part. There are some things that went very well for us," Rivera said. "Some of us are a little bit rusty. Believe me, we weren't mistake-free.

"I'd like to believe they understand the sense of urgency. We play in 107 days. We need to get better every time we get on the football field."

The Panthers are 107 days from visiting the Denver Broncos to kick off the 2016 NFL season with a rematch of Super Bowl 50, but Rivera doesn't want his team thinking about the past. The Panthers return nearly all the players that helped them go 15-1 last season, but the beginning of that run can be traced back to OTAs.

"The message is that you don't start where you finished; you start from the beginning," Rivera said. "You can't become complacent. It's easy to feel all the pats on the back and listen to what everybody says. But we've got to stay focused if we want to attain our goal."

In 257 days, Super Bowl LI kicks off in Houston.

"You've got to love the grind. You've got to love being out here with your guys," safety Tre Boston said. "There's nothing I'd rather do."

2. CONFIDENCE IN CAM: When asked about quarterback Cam Newton's first OTA, Rivera called him rusty. Rivera said Newton, like Carolina's other quarterbacks, had a few poor passes and made a couple of costly decisions.

Part of Rivera's assessment might have to do with the lofty expectations he has for the league's reigning MVP.

"I'm challenging him. He can become a better football player," Rivera said. "He's such a dynamic football player athletically and mentally that every time he gets out here, he can improve. He can become better."

The idea that Newton – the first quarterback in NFL history with more than 100 touchdown passes (117) and 25 rushing touchdowns (43) in his first five seasons - might still be developing has to be scary for the rest of the NFL.

3. THREE MISS FIRST OTA: Newton was without No. 1 wide receiver Kelvin Benjamin, but it didn't have anything to do with the knee injury that sidelined Benjamin all of last season.

Benjamin, defensive tackle Paul Soliai and kicker Graham Gano missed the first OTA for personal reasons.

"We had a group of guys who had some personal issues they had to take care of back home. They were excused," Rivera said. "Not that they needed to because it is voluntary, but they came in and informed me that they had some personal family issues they needed to attend to."

4. INJURED PLAYERS PARTIALLY PARTICIPATE: While Benjamin didn't practice, the Panthers were thrilled to see wide receiver Stephen Hill, who suffered a horrific knee injury in training camp last year, on the practice field.

Hill, along with cornerback Bene Benwikere (leg) and five players recovering from offseason shoulder surgeries – including linebacker Luke Kuechly - took part installation periods and some individual periods but not in team periods.

With Benjamin and Hill not taking part in the scrimmage-like portions of practice, wide receiver Brenton Bersin emerged as Newton's favorite target on the first day. Newton may have looked to Bersin one time too many, however, as linebacker Shaq Thompson stepped in the path of a pass bound for Bersin and returned it down the sideline.

5. TOP DRAFT PICK DEBUTS: Defensive tackle Vernon Butler, the Panthers' first-round pick in the 2016 NFL Draft, got his first chance to play with and against Carolina's veterans.

"It was good to be out there with guys I've watched on TV," Butler said. "The next step is getting better so I can help the team out with my ability."

Butler missed a couple of plays to get his leg checked out after an early play but returned and declared himself fine after practice.

"He got back in a little bit afterwards. That was nice to see," Rivera said. "He did a couple of really nice things, showed some explosiveness out there."