Walker had the more exciting day of the two backup quarterbacks vying for the No. 2 job behind Sam Darnold, with an accidental touchdown pass Walker wasn't even supposed to throw.
Panthers head coach Matt Rhule said Walker wasn't supposed to snap the ball at all, hoping to draw the Colts offside. Instead, he snapped it, and then weirdness followed.
"I heard a whole bunch of things in my headset, and I heard him yelling from the sideline," Walker said of Rhule.
"It worked," Walker said with a grin. "I saw Omar's guy stopped covering him, and once he broke in, I saw Tommy running full speed across the field, and he was the one who happened to get hit in the chest with the ball."
The play underscored the kind of freewheeling Walker has a knack for, though they'd like him to show more discipline at times.
Rhule said he talked to Walker about being aware of his position on the field, saying he thought Walker could have run for a touchdown or at least a first down on a play he tried to force to Terrace Marshall Jr. That was nearly intercepted, and the Panthers settled for a field goal after a turnover.
But Walker said, on the whole, he felt more comfortable than when he played for the Colts a couple of years ago.
"Just me having fun, to be honest," he said of the difference in his game. "When I was here, I didn't have as much fun playing football, to be honest. I was always thinking. I'm not thinking as much anymore, just going out there and playing.
"Trusting my teammates and going out and trying to put the ball in my playmakers' hands. That's something I lacked when I played here, and now I'm here and have an opportunity to find guys and put it in their hands."
Walker finished the day 10-of-21 for 161 yards and a touchdown, a number inflated by a 60-yard pass to Marshall.
Grier didn't get as many opportunities, and Rhule said part of that was a function of nursing a lead in the second half.
The Colts also put together a long game-winning field goal drive, keeping Grier from having much of a final chance. Still, after not playing in an actual game since late in 2019, Grier wasn't taking anything for granted.
"It felt great to get tackled again since it had been a couple of years," Grier said. "Felt great. It's good to get those live reps and get back into it. It's definitely different, and you can try to mimic it as much as possible, but it's just different. So it's good to get those live reps.
"I felt good. I felt comfortable. I felt a lot more comfortable than I did in 2019."
The game's late stages took on a late-2019 quality, as three straight false start penalties — the third one on "everyone but the center," according to referee John Hussey — put the Panthers in a third-and-17 situation. Grier joked about the "18 false start penalties," and it seemed like he might have been right.
Grier said he wishes he'd have stayed back in the pocket and tried to set himself more before that pass, but was generally pleased with his work on the day. He finished 6-of-10 for 31 passing yards.
"I think I did a good job of executing the play that was called," Grier said. "I think they did a good job of the end of the game with a long drive and a field goal, and they didn't leave any time.
"So yeah, sometimes that's the way the game works out. I'm not a big personal guy. I'm a team guy, want the team to win, and want to run what's called."
Grier said Rhule assured him he'd get chances, and Rhule said afterward that he hadn't firmed up a plan for the remaining two preseason games.
The Panthers rested Darnold and all the starters, and haven't decided if they'll play at all next weekend against the Ravens.
The Panthers have some immediate concerns before that, as they have to monitor a few injury situations and make the first five cuts of the offseason.
Cornerback Troy Pride Jr. was carted off with a knee injury, and Rhule didn't have an update on his status after the game.
The Panthers have to reduce the roster from 90 to 85 by Tuesday.
That's when they return to Spartanburg for the final week of training camp, which includes two days of joint practices with the Ravens.
View photos from Indianapolis as the Panthers take on the Colts in the first preseason game.