So, I'm writing this movie after seeing 7.9 ratings, which I feel is very biased for this movie.
I will come to the point that this is an average movie that claims to be sport-comedy, but there's nothing sporty about this movie.
Half the time, it felt like they were playing Rugby, not Football. The Homeless Soccer Tournament was a big joke as there were no rules on fouls and penalties.
Coming to the acting, Park Seo Joon and IU both were good and were ably supported by the rest of the cast. But that's it. They were just good and not even once went beyond that.
But the main criticism is there's no character development. It seems like they have put a bunch of sob stories expecting to gain sympathy from the audience. It doesn't work in this era, maybe in the 80s and 90s but not now.
Giving sob stories is fine but you have to show their character development and this was hardly true for any of the characters. And as for the comedy, there were a few hits and misses, mostly misses. It only made me smile, not made me laugh, which I think is a must for a movie marketed as "sports-comedy".

Overall, a better effort was required from all, the director, the writer and the actors.