Sports weight management come under two main areas. 

1. Weight Management for better performance
2. Weight Management for fat reduction

Weight Management for better performance can be the guise of supporting an ideal playing or competing weight for an event or competition. 

Keeping your weight at a constant level can be difficult for some, for example over a rugby season it is not uncommon for players to lose weight (and muscle) as the more training and playing time racks up, so extra weight is shed. For a prop, who rely on their strength this can be problematic. 
Vice versa, someone training for their first half marathon may desire to lose a few kilograms as that extra weight is just ‘dead weight’ and is only a hindrance to their performance and enjoyment. Being lighter also put less stress on joints and bones, and a study of participants competing in the Kona Ironman showed that on average, the athletes with the lowest level of fat percentages completed the event faster. 

A common supplement for weight management is a protein powder, either with extra carbs (to keep weight on) or without carbs (to keep weight off). 

Weight Management for fat reduction is more about appearance. These would be more associated with gym goers and/or cross fit participants. These athletes may be after that ripped look or desire a six pack, so stripping fat from the body is paramount their sporting goals. 

If you think you fall into this category then again a protein supplement could be beneficial as well as possible a supplement that support fat metabolism like Garcinia Cambogia, Hoodia, Green Coffee Bean or L-Carnitine. Also to consider are products containing Chromium as they support insulin levels, another factor in supporting weight control.