After having a break-out season in 2016–17, Marchand intended to double down on his consistent offensive production for the 2017–18 NHL season. His athletic abilities that season, however, were largely overshadowed by his on-ice behaviour. In January 2018, Marchand received a five-game suspension from the NHL for an elbow to the head of Devils skater Marcus Johansson, who suffered a concussion from the play. It was the ninth time that Marchand had received either a fine or suspension from the Department of Player Safety. Despite the 2018 All-Star Game taking place in the midst of Marchand's suspension, he was allowed to take part in the game and skills competition at Amalie Arena, where he was subject to booing from fans in attendance. On March 9, 2018, after receiving a previous warning about embellishing his reaction to a hit in an attempt to draw penalties, Marchand was fined $2,000 for embellishing a tripping penalty by Olli Maatta of the Penguins. The following day, Marchand collided with Blackhawks skater Anthony Duclair, causing the latter a season-ending leg injury. Duclair told reporters that Marchand had reached out to him after the injury, but that it was still a "pretty dirty" play. On April 2, Marchand received his second fine in the span of a month, with a $5,000 penalty for cross-checking Andrew MacDonald of the Philadelphia Flyers. That same season, Marchand scored the third hat trick of his career with an overtime shot against the Red Wings. The last goal was also his 11th regular-season overtime goal, passing Glen Murray's record for the most among the Bruins since overtime was reinstated during the 1983-84 NHL season. Marchand took home the Elizabeth C. Dufresne Trophy for the second year in a row, and was moved from the Bruins' Third Star to Second at the end-of-year awards ceremony.