Ball Side is another term for ‘Strong Side’ in basketball.
It's the area that contains the player with the ball and their teammates, as well as the defenders guarding them. The strong side is important because it helps players position themselves correctly on the court. The division is done lengthwise.
Using the term "strong side" makes communication easier for the team, since the ball is always moving and the left and right sides can change quickly.
When a coach or teammate yells "strong side," everyone knows to focus on the side of the court where the ball is. This allows the players to adjust their positions based on the current location of the ball.
Basketball Terminology (Strong Side) - [Ball Side][1]
[1]: https://www.youtube.com/watch?v=cC30-RT4Fnw