The phrase "top flight" means being among the very best or highest level in a particular field or category. It refers to being at the top or above the average. Full definition
It wasn't his first season in top flight football, and the errors had more to do with how down on confidence he was, than his football skills. (anfieldindex.com)
Regardless of their misery, I have never seen English top flight division so poor when it comes to the top teams. (justarsenal.com)
They have conceded at a rate of exactly two goals per game in the Spanish top flight so far and 71 % of their road games have gone above the 2.5 goal line. (football-bookmakers.com)