Yes—there are purpose-made eye shields used by target shooters, often sold as a patch or blinder that attaches to glasses or a visor. They block light to the non-viewfinder eye while letting you keep both eyes open, which can reduce strain.

That said, for sports photography, several photographers recommend keeping both eyes open without fully blocking situational awareness. Your free eye helps you follow moving subjects, reacquire them if they leave the frame, and more importantly stay aware of players rushing toward the sideline. That can be a real safety advantage.

So the practical options are:

• use a shooting-glasses eye patch/blinder attached to glasses or a cap
• keep both eyes open if possible, especially on the sidelines for tracking and safety

If you try a blinder, choose one that blocks glare but doesn’t overly reduce your awareness of the action around you.