What you do is shove your arm down their throat as far as possible, so they will choke to death on it. People have survived bear attacks this way, I am sure it works for lions also
DO NOT FOLLOW THE QUOTED ADVICE
It doesn't, lions are much more calculated with their bite angle than bears are. Bears have long,snouted mouths and are not as intelligent with how they use their hands and mouth in a fight, lions are extremely adept at the angle of their bites. They will notice you trying to put your arm into their mouth and use their front paws to pull your arm away, this is a habit they have with any/all fights vs armed/legged beings when biting them.
If you watch a lion/lioness hunting a creature with long limbs (so basically something taller than a warthog), they 'tuck in' the front legs of the creature and use their own hind legs to both balance and immobilise the prey's hind legs, tripping them up tactically. A lion will not fall for you trying to punch its throat, it truly will end with you mauled beyond repair at best or you dead at worst.
Lions are extremely emotionally reactive creatures in a sadistic manner. If you show fear, they respond with aggression, if you show too much aggression their version of fear includes aggression anyway, only calm with confidence settles them.