The fact that so many of you don't understand the usage of this trope is honestly pretty sad. Yes, it is cliche, but it has an important usage in this story. This is not a situation where 'man has to save helpless woman', but is instead a trust and reliability litmus test for the characters.
Clearly, Tsuruse said in her internal dialouge that she deals with these situations from time to time, so she doesn't normally need help to take care of pick-up artists. However, due to her lack of sleep she simply can't muster up her normal strength or ferocity to deal with it, which is why Tsukinawa steps in. Which is important for him to display that he's not just a cute face, but can also take care of problems on his own (even if Tsuruse wouldn't normally need help). Plus, it gives the author a chance to make the cute male lead look manly and badass. Additionally, you guys are underestimating Japan's nampa (pick-up artist) 'culture', and their desire to not get involved in the trouble of others.
I'm betting on he is a current or former martial artist or something else. Tsuruse did say previously that he seemed to have a toned/trained body.