I think a horizontal jump is perfectly fine. It should have reduced height compared to normal vaulting( may be for obstacles of about knee hight). And if you try to jump over obstacles higher than that height, you will be tripped over and fall on the ground( but you are still able to cross the obstacles, just with your face hitting the ground afterwards). And if the obstacle is way too high, than you hit that obstacle,bonce back and fall on the ground. The animation of tripping over may be the same as being run over by vehicle, coupled with free falling and inertia. It is absolutely logical for people trying to jump over obstacles when bullets are incoming, it is better to get tripped over than shot.