Ishmel Demontagnac became the fourth Cobblers player to be sent off this season during the club's 2-0 defeat to MK Dons in the Johnstone's Paint Trophy on Wednesday.
However, Boothroyd believes that the players have been harshly punished.
"Everybody has to take responsibility. But this is the only red card we should've had this season. They've got to go in for tackles or I'm going to get annoyed with them," Boothroyd told BBC Radio Northampton.
"Tackles have gone out of the game now. Sometimes players are over-keen to do well, which is a good bad thing, and referees are too quick to get the cards out."
Northampton have also had 13 players booked this campaign.