why is this a poor model for hitting a baseball?

y = -0.002x^2 + 0.879x + 3.981

I know it gets hit at approx. 4 feet high. The -a gives the right shape like a hill. There's a -4.48 and 443.95 zero, which can be hit for distance. The max is (219.75, 100) so that seems doable. What am i missing?

Your wequation can be rewritten

y = -0.002(x^2 -439.5x +48290) +95.58 +3.981
= -0.002*(x-219.75)^2 + 99.56

It looks OK to me .