White slime-like, possible like mucous, buildup on my mouth during sports? i maintain hydrated, so what else could be the cause?

Post nasal drip?: Does this interfere with exercise? Is there shortness of breath? Cough? If not, another possibility is that during your exercise, running, jumping or core-based exercise is causing stomach contents to splash up your esophagus; this irritation can trigger mucus build up in the back of your throat. Try watching what you eat or drink just before exercise. Avoid tea, lemon water and acidic drinks.