Playing basketball is permissible as long as there are no forbidden things being committed. Their shorts are covering the Awrah which means that we don’t have a problem with the dress code.
The problem is with the concept of playing professionally in the NBA with all the music, mixing between the men and women and with playing with and against the disbelievers. There are a lot of gambling involved and you will be part of it whether you like it or not.
Is it a Muslim’s objective in life to play in the NBA?
Allah has created us to worship Him. Your dreams should revolve on this.
If you notice, you will find that you are fond of people like Koby Bryant or Lebron James yet they don’t pay attention to the fact that they are not Muslims.
I am not telling you not to pursuit your dreams but I am telling you to have the right dreams that would benefit you, your religion and your community and people.
And Allah knows best