Would a football mouth guard help with jaw clenching at night?

Probably not: But it would prevent damage from grinding. Talk to your dentist if you are clenching. A custom made full coverage splint is best. Partial coverage splints create problems.

Maybe: A soft type athletic mouthguard can be used to lessen the affects of clenching at night. However, i prefer a different type of mouth guard/occlusal guard to protect the teeth/jaw for a clenching habit.

Unlikely: Possible but unlikely. You can try it. No harm done. With such an ill fitting apparatus, may would clench more. Consider a custom device by your dentist. Clenching can lead to TMJ (jaw joint) problems.

Depends: If it is a custom made upper only (made by your Dentist), then it may help by cushioning the clenching. However if any other kind, it may make things worse. See your Dentist for a custom occlusal guard and possible restoration of any worn tooth edges and possible bite adjustment. Good Luck.

Avoid soft: It can stimulate an increase the jaw clenching at night. Hard acrylic custom night guard for teeth grinding: professionally made is recommended.