Can one leg and foot swell and go red from a groin adductor strain?

Not likely: Unilateral swelling of foot and leg is worrisome and suggests vein pathology such as phlebitis(blood clot) or chronic venous insufficiency. A groin strain wouldn't cause this, but inflamed or enlarged lymph nodes in the groin could. Get a venous ultrasound of that leg and have a careful examination of the groin and leg by your physician or a vascular surgeon.