What purpose would Ian fighting Axel outside of MMA? From what I've seen Axel's obsession with Lena seems to have lessened. I don't think Ian will need to protect any of the girls from him. Unless beating him in MMA is what you mean.
Axel's obsession with Lena can only be ended in a route that I don't remember how I got there. The point is that if you take that route, Axel apologizes to Lena and thanks her for talking to him, which allowed him to close that cycle and move on from the breakup of their relationship before she leaves for Perry's summer house in chapter 12.
The first scenario is the simplest: Axel, still obsessed with Lena, decides to talk to her one way or another, and that will cause Ian to intervene again, leading to a fight like the one outside the Blazer, but this time Lena won't be able to stop the conflict.
The second scenario is Cindy's route. If you decided not to set limits for Cindy in the relationship, this will end up causing her to cheat on Ian with Axel, which will obviously anger Ian and cause a fight with Axel.
The third scenario involves Cindy again, but this time it would be Wade's fault. This scenario would only be possible if you decided not to help Wade break up with Cindy. Let's say that by chance, the guys go to a party to cheer Wade up or celebrate something, and at that party, they find Cindy and Axel. Wade, still depressed and drunk, decides to confront Cindy and Axel for what they did, which escalates until Axel decides to hit Wade and Ian decides to intervene.