Huh? Tell me you are joking.Sure, if you apply uneven force. If you apply even force, there is no deformation.
An even force applied to the entire surface of a perfect sphere most certainly deforms! This is the exact principle on which the atomic bomb is based!
And as Pete pointed out, there is no even force applied here. There is an applied force on one half of an object, which can hardly be considered even. In fact, it's as lobsided as can be.
Now, as far as deformation causing spin is concerned, I am in agreement with you (shock, horror). Let's for argument's sake say that a paintball is perfectly spherical. When a force is applied all over one half of this sphere, this will cause a deformation that is predictable, rather than random. In other words, when looked at from the front (i.e. the exit end of a barrel), the ball will be symmetrical. So the face of the deformed (to whaterever extend) ball that is presented to the outside force (drag), will be suffering from equal amounts of drag all over, meaning no spin. No argument there. I never said it would.
Depending on many random factors, like how the seem on a paintball will "fall" into the breech of the gun, a slight amount of spin may occur, but not enough to do anything meaningful.
If we were to bring back the good old rifled Armson barrels however...