He played in the National Hockey League (NHL) for the Los Angeles Kings, Philadelphia Flyers, Nashville Predators, New Jersey Devils, Buffalo Sabres, and Toronto Maple Leafs between 2008 and 2023.[10] Entering his second NHL season, Simmonds was looking to increase his offensive production, having tied for the Kings' goal-scoring lead in pre-season play that year.[13] On June 23, 2011, Simmonds was traded to the Philadelphia Flyers (along with Brayden Schenn and a second-round pick in the 2012 NHL Entry Draft) in exchange for Mike Richards and Rob Bordson.[15] On September 22, 2011, during a pre-season game in London, Ontario, between the Detroit Red Wings and the Flyers, a banana was thrown onto the ice while Simmonds was making a shootout attempt.[20] On March 30, 2012, against the Ottawa Senators, Flyers center Brayden Schenn shot a puck which glanced off of Simmonds' forehead and into the net.In a game between Liberec and Piráti Chomutov in the Czech Extraliga, fans began a chant of "opice", a term which roughly translates to "monkey", towards Simmonds, after his involvement in a fight.[23] On February 20, 2013, Simmonds recorded another Gordie Howe hat trick in a 6–5 win against the Pittsburgh Penguins at the Consol Energy Center[24] when he scored a goal and an assist and fought Tanner Glass.[29] On February 25, 2019, the Flyers traded Simmonds to the Nashville Predators in exchange for forward Ryan Hartman, as well as a conditional fourth-round selection in the 2020 NHL Entry Draft.[30] He was part of a larger series of trade deadline moves that Nashville made in order to increase their presence on the power play, as well as their overall physicality, both of which had been struggles for the team during the 2018–19 season.[31] Simmonds joined the Predators with a 16-game goalless drought, which carried over to another eight games in Nashville before he scored in a 3–0 victory over the Toronto Maple Leafs on March 20.[33] He left Game 2 of the first-round playoff series against the Dallas Stars after being hit in the knee with a slapshot from teammate Roman Josi, and was considered week-to-week.[35] Between Philadelphia and Nashville, Simmonds put up 17 goals and 30 points in 79 games, and he was the NHL's 2019 recipient of the Mark Messier Leadership Award, given to a community leader both on and off the ice.[41] Although he maintained interest in staying with Buffalo, Simmonds was allowed to court offers from other NHL teams prior to the opening of the free agent market on October 9, 2020.