Seattle cornerback Richard Sherman and 49ers receiver Michael Crabtree don't like each other.

The mutual dislike began long before the Seahawks beat the 49ers 23-17 Sunday in the NFC Championship game -- long before Crabtree took issue last week with the notion that Sherman is the best cornerback in the NFL.

Their feud began last season during on-field encounters and escalated during an offseason incident at a charity event hosted by Arizona Cardinals receiver Larry Fitzgerald.

The incident was first reported by the Seattle Times on Sunday night in the wake of Sherman's postgame rant about Crabtree on FOX, and Sherman later made brief reference to the incident in a first-person column for SI.com.

But Sherman's brother, Branton, provided details of the incident Monday to this newspaper.

Branton Sherman did not witness the encounter firsthand. The description below is based on Sherman's recounting in a private conversation with his brother.

"Richard was at the charity event with people like Snoop Dog and (former 49ers receiver) Kyle Williams,'' Branton Sherman said. "Richard's a friendly guy, and he saw them sitting around a pool and went over to shake everyone's hand.

"When he got to Crabtree, Crabtree slapped Richard's hand away and stood up like he wanted to fight. Everyone was like, 'Calm down, Crabtree.' Richard said, 'Why are you tripping out. We're off the field.'

"Crabtree wanted to fight but everyone got in the way and backed him down.

"Richard told me about it down the road. He told me he would do Crabtree in the media, and he did. (FOX) caught him right after the game.

"They have a personal vendetta against each other."

Reached Monday morning, Williams acknowledged that he attended the charity event.

The former Arizona State receiver considers Crabtree to be "like a brother" and has known Sherman, a Stanford graduate, since they played against each other in college five years ago.

"I'm not going to get into specifics,'' Williams said. "Those guys" — Richard and Branton Sherman — "can say whatever they want.

"To me, what happened (Sunday) was nothing more than two guys who are passionate about what they do and are at the top of their games at their respective positions. It's a rivalry that's going to continue to build.

"That's what you're seeing: Passion.

"Richard called him out 100 percent. (Crabtree) will respond. He'll work hard and make sure he's ready to respond on the field."

Crabtree declined to talk reporters gathered in Santa Clara on Monday.