Singletary didn't provide details about the incident, but said it was non-football related and is closed. He met with both players immediately in the locker room and they returned to practice separately.
"How many of you guys have families?" Singletary said to reporters. "You mind raising your hands? You scared to raise your hands? So you have kids and every now and then your kids have some misunderstandings or what have you and they forget that there is a father at home.
"I will not talk about the issue. But I will talk about this: They were both wrong. And we will not have distractions on this team. Vernon just forgot temporarily, and that is not allowed."
Neither Crabtree nor Davis spoke about the incident. Both have been sidelined this preseason because of injuries and Singletary ruled out Davis for Thursday night's preseason finale against San Diego.
Crabtree's status is uncertain. The second-year receiver is nursing a neck injury and hasn't addressed it or spoken formally since the start of camp Aug. 1, declining multiple media requests. Yet the 49ers' website posted a lengthy story quoting him Tuesday afternoon.
"I appreciate Vernon speaking from his heart, but it was just wrong," Singletary said. "But he indeed is every bit the reason why I made him captain. He's not going to sugarcoat things. He doesn't know how to sugarcoat things. But I appreciate what he was striving to do, but it was just wrong."
Davis had developed a reputation for scuffling in training camp, but was determined not to have any issues this year. He's coming off a Pro Bowl season in which he tied Antonio Gates' touchdown record by a tight end with 13. The 26-year-old Davis is still a captain.
Crabtree has long been known as a diva dating to his Texas Tech days. He was the Niners' 10th overall pick in the 2009 NFL draft, then didn't sign until October following a 71-day contract stalemate.
Singletary felt the incident between Davis and Crabtree made the 49ers stronger.
"We didn't get better on the field in practice, but we got better as a team," Singletary said. "There are no elephants in the room. The elephant was exposed."