Can someone make you lag even after leaving the match?

[Tommy154]

Was playing rocket league and some guy was mad he was losing and typed in the chat he was gonna lag switch next round, and he did and my ping was insane. And the game eventually dropped me. But then my internet was still lagging like crazy even after I reset my modem. Am I being attacked or something?

 

[James Mason]

Possibly, this could be if Rocket League isn't protecting your IP, contact them.
League of Legends has/had similar issues.