Crossing the floor: Wikipedia
In politics, crossing the floor is when a politician changes their allegiance or votes against their party in a Westminster system parliament. Crossing the floor may be voting against the approved party lines, or changing to a second party after being elected to a first party.
In video from the House, Trudeau is seen walking toward Brown in a crowd of MPs in the Commons aisle, taking his arm in an apparent effort to move Brown toward his seat. While doing so, he encountered Brosseau, who was also standing in the aisle and was seen physically reacting after the contact.
"I was trying to start the vote, the prime minister grabbed my arm. I immediately told the prime minister to let go of me — now," Brown said in a statement released later. "Immediately afterward, the prime minister went back down the aisle of the House to confront other members of opposition parties."
"I later told the prime minister he should NOT have gotten out of his seat," Brown added.