Erik ten Hag has called on his Manchester United players to "play smart but nasty".
United saw a four-game Premier League winning run ended by a humiliating 6-3 defeat by Manchester City on Sunday.
Ten Hag's sixth-placed side have received 23 bookings in seven games his season - the second most in the league.
"I know nasty," Ten Hag said. "I know what nasty is. I think also in that matter we can progress. Sometimes also play a little bit more smart."
The Dutch manager added: "We have too many bookings and some in the start [of matches]. I heard in the Premier League they will play tough but I'm really wondering why we collect so many bookings. I don't understand."
Only Nottingham Forest (24) have accumulated more yellow cards than United in the English top-flight this term.
Portuguese right-back Diogo Dalot earned a team-high fourth booking after just two minutes in Sunday's Manchester derby loss.
"The first booking on Sunday, I really don't understand that. We want to play tough, we want to keep the game going," Ten Hag said.
"Then in the second minute already it's a booking. I think it's a duel, clear it was a foul, but to then get booked? Also I saw many other bookings where I think 'OK, is that necessary'?
"But also I take it to the players. I have to keep the mirror [on them] that they have to play smart, but also they have to play nasty as well."