Is it a good option to have a sort of sport-related extracurricular, regardless of whether you are aiming for a sports degree (e.g. part of a local soccer/football club, or a volunteer swimming coach)? Is it a good option?
Extracurriculars do not form a major portion of the UK admissions checklist. Admissions officers usually look for extracurriculars that directly relate to the program of study you are applying for. While it is always good to be involved in sports and demonstrate your interest, it might not directly have an impact on your application.
You can learn more from this ebook on supercurriculars for UK admissions.