Can you tell me what you suggest if a person has a schizoid personality disorder, would they be interested in playing sports, like boxing?

Perhaps: Personality disorders are not 'exact' diagnoses - nearly no psych DX is. Many physical are not either. So, a person could be 'pretty' much schizoid - even meet the criteria, but have a unique aspect. Also, boxing is not very social ; fitness workouts can let you ignore others if you wish. Try not to think of 'having' it , like diabetes, etc. - it's just a best fit description of personality.

Not likely: The hallmark of the schizoid personality disorder is an indifference to interpersonal relationships. In plain English, these folks prefer to be alone much of the time, and are not lonely because of it.