Players are required to wear business casual attire whenever they are engaged in team or league business, with a few exceptions.

Business casual attire: A long- or short-sleeved dress shirt (collared or turtleneck), and/or a sweater. Dress slacks, khaki pants or dress jeans. Appropriate shoes and socks, including dress shoes, dress boots or other presentable shoes, but not including sneakers, sandals, flip-flops or work boots.

Team or league business: All activity conducted on behalf of the team or the league during which the player is seen by, or interacts with, fans, business partners, members of the public, the media or other third parties. This includes arriving at games, leaving games, attending games when not in uniform, participating in team or league events, conducting media interviews and making promotional or other appearances.

Exceptions: Players who are in attendance at games but not in uniform must wear a sport coat and dress shoes or boots and socks when on the bench or in the stands during the game. Players leaving the arena may wear either business casual attire or neat warm-up suits issued by their teams. Teams can make exceptions for special events or player appearances where other attire is appropriate, such as participation in a basketball clinic.

Not allowed while on team or league business: Sleeveless shirts. Shorts. T-shirts, jerseys or sports apparel (unless appropriate for the event, team-identified, and approved by the team). Headgear of any kind while a player is on the bench or in the stands at a game, during media interviews or during a team or league event or appearance. Chains, pendants or medallions worn over the player's clothes. Sunglasses while indoors. Headphones (other than on the team bus or plane, or in the team locker room).

Source: NBA