out of gas, timing off. bad plug, safety stop still on, bent or sheared keyway,
starving for fuel
dirty carb bowl or water in the carb
Blocked air filter, need spark plug replacement,
did you check and make sure you have plenty of oil. or maybe your lawn mower just needs a break.
make sure the gas valve is turned on and you put the air filter in right
your electric motor(I assume) probably wont have enough torque, That is on a Riding type mower, not a push mower, it might work on a push mower as long as its not self prepelled, because your motor probably still wont have enough torque!
replace it
bad bearing
replace battery & starter solenoid.. possibly carb.
you should give enough space between you and the horse so that if the horse kicks you will not be in the way, and you wont get hurt
get a new one
Horses have a blind spot right behind them, so its important that you let them know you are behind them so that they dont spook and try to kick you. The best thing to do would be to walk calmly behind them, talking to them in a calm voice, and gliding your hand over their rump as you walk past. If you dont have much room, walk very very close to the horse so that if they do kick, you wont get the full impact.