Well, if you allow scenarios like that, anything can happen.
Scenario 1.
Spearman throws a spear into the sky hitting a bird which spins out of control and into the barrel of the tank causing it to clog at the moment they fire thereby exploding the tank.
Scenario 2.
Spearman gets a hold of a CD player and blasts Ricky Martin thereby causing the tank driver to go insane and kill himself.
But honestly, you just have to assume that they fight, not they do some weird ninja crap. If straight up fights weren't the case, then even a worker could defeat a tank given the right circumstances.
Anyone play Master Of Orion 2? That had it right, if you were the ultra elite super tech gods, then you could build machines to crush your opponent. Simply put, a Doomstar class ship with Death Rays would never be beat by a Scout class ship with a Laser Cannon. Too think the scout should have a chance means you've been watching too much Star Wars, not every unit has some special weakness that can be exploited.
Oh well, I'm just disgruntled because I lose a buttload of battles that I should rightly win thereby eliminating the option for me to play a military game.