Professional sports betters absolutely think in probabilistic terms -- "I think there's a 25% chance we'll win, the market thinks there's a 20% chance we'll win

Professional sports betters absolutely think in probabilistic terms -- "I think there's a 25% chance we'll win, the market thinks there's a 20% chance we'll win" etc. Kelly bet sizing absolutely makes sense, though market depth and Bayesian uncertainty also act to reduce bet sizes.