In Tangerine, what reason does Mr. Fisher give Paul for being so wrapped up in Erik's football season and forgetting about Paul's soccer success?

Mr. Fisher remarks that he focuses on Erik due to the particular importance of his  football season. Since Mr. Fisher wants Erik to play competitive college football in order to enter the NFL, this season is like a job interview for football superstardom. It's important that scouts for big-time football schools see Erik play well. 

Paul counters his dad’s argument by pointing out that while Erik is playing competitive football, Paul is also playing competitive soccer. Mr. Fisher...

Mr. Fisher remarks that he focuses on Erik due to the particular importance of his  football season. Since Mr. Fisher wants Erik to play competitive college football in order to enter the NFL, this season is like a job interview for football superstardom. It's important that scouts for big-time football schools see Erik play well. 

Paul counters his dad’s argument by pointing out that while Erik is playing competitive football, Paul is also playing competitive soccer. Mr. Fisher seems unaware that the two sports seasons overlap. Even if Mr. Fisher invests most of his time in Erik's season, he could still attend Paul's most important games. The reader immediately notices the unfairness of Mr. Fisher's singular focus since Paul has been playing for the Tangerine Middle School War Eagles, a highly regarded and undefeated  team. In fact, Paul recently helped the War Eagles win their championship game by playing a good game in goal (even though he almost flubbed the last penalty shot). Paul’s teammates and perhaps even Paul himself could easily have a chance at playing college and professional soccer. Mr. Fisher doesn’t recognize this possibility.

Paul's question is justified. Paul is rarely alone with his dad, and from this, the reader infers that Mr. Fisher rarely takes an independent interest in his second son’s hobbies, goals, and successes. While Paul’s mom cheers him on during his intense soccer season, Mr. Fisher doesn’t even attend the nail-biting championship game. Instead, he attends every football practice and competes with the other fathers to become one of the favored Lake Windsor Downs High School “football dads.”  This strange and unfair behavior stems from Mr. Fisher’s over-investment in Erik’s future career. Mr. Fisher shows extreme favoritism towards Erik, his eldest son. As Paul states over and over again, Mr. Fisher is trapped by the “Erik Fisher Football Dream,” his fanatical wish for Erik to play for a Division I college team and enter the NFL.

Your question leads to one of Tangerine’s essential questions: how can a good person, a normal guy like Mr. Fisher, completely abandon his principles for the sake of a game? Why does the “Erik Fisher Football Dream” have the power to make Mr. Fisher act so callously towards Paul?  This mania doesn’t just infect Mr. Fisher; it poisons the entire town of Tangerine. For example, the Lake Windsor Downs counselor tells Mrs. Fisher that Erik’s grades will improve after football season. Football is a justified excuse for poor academics. Even more bizarrely, football is an excuse for breaking the law since the Lake Windsor Downs team lies about Antoine Thomas’s eligibility and puts his future at stake. Football’s also an excuse for putting kids’ lives at risk since the coaches and parents willfully ignore the lightning risk that claimed Mike Costello’s life at practice. In summary, the adults in Tangerine are blinded by football, and Mr. Fisher’s willful ignorance of Paul’s soccer season is just a symptom of a much bigger problem.