Last Wednesday, he prevented a robbery after an early-morning visit to a North Carolina Walmart, helping the police capture a male suspect in the process. On Monday, he delivered a solid effort in his full-season debut for Class A Greensboro.
The woman he saved, April Davis, was on hand to see the right-handed Marlins prospect allow one earned run on two hits over five innings in the Grasshoppers' eventual 11-6 loss to visiting Delmarva.
"The lady was really nice. He shook her up a bit," Petersen said. "It was good to see her."
Petersen had just finished shopping in the Wal-Mart when he saw suspect Andrew F. Conrad Jr. grab Davis' purse and keys and throw her to the ground. Davis called to Petersen for help and as he chased him, Conrad allegedly dropped the purse and tried to get into Davis' car.
"I grabbed him around the stomach and kind of held on to him," Petersen said. "He was squirming, so I kind of held him around the neck in sort of a choke hold. He threw back the keys and said, 'Just let me go.' I said, 'I don't think so.' I had to hold on to him for a while."
Greensboro police then arrived on the scene and apprehended Conrad, Petersen said.
"It was pure instinct, pure adrenaline," Petersen said. "It was kind of dangerous. It turned out the guy was kind of wanted."
The rush was somewhat different than what happens on the mound, he said.
"On the mound, you have time to think," he said. "There was no thinking (Wednesday). If he had a gun or a knife, it could have been more stupid (for me)."
After coming through the incident unscathed, Petersen was ready to make his debut Monday.
"I felt good," he said. "The fastball is not there yet, but my curve and changeup were working. I pitched downhill. It was respectable."
In his first full season, Petersen knows there's a long road ahead and time to improve.
"I want to get hitters out earlier in counts in a long, long season," he said. "I may not have as many strikeouts. Get some ground balls, go for easy outs and hopefully pitch deep into games."
And he won't be taking his instincts for granted either.
"It was crazy, I never go through the self-checkout (at Walmart), but I had this feeling I should do that. I had this feeling in my gut."