How does the momentum of a 75 kilogram stationary football player compare with that of a 70 kilogram player moving at a velocity of 6 meters/second?

An object's momentum is the product of (its mass) multiplied by (its speed).  So we really don't need to do any calculating to answer this question.  

If speed is zero than the product is zero.  

An object that's not moving has no momentum, no matter how much mass it has.  

So a mosquito in flight has more momentum than the 75 kg football player sitting on the bench or asleep in the locker room.