How can I help my son with dyspraxia play sports with his friends?

Practice. Work with him on his weaknesses, practice practice practice, focus on sports that he can keep up with better. Compare him to him only, and make note how he is doing better this week compared to last. Depending on the ages, it may be good to talk with the parents of some of his friends to explain to their kids to be patient with him and encourage him.
Help with sports. If you mean by dyspraxia - clumsiness with fine and gross motor activities, avoid small ball games such as baseball. Stick to games like soccer, running, especially the races for kids. Chess, checkers, swimming, some video games that require more than one person to play, golf. Avoid him being goalie. Since goalies are very likely to be criticised when the other team scores.