I think a 1st level Fighter should be able to take 3 hits from an average weapon and keep fighting, but be dropped by the 4th hit, assuming he has average Con mods to HP.
Or to put it differently,:
Assuming an average weapon does 1d8 damage x2 crit, the Fighter L1 has X HP, where 3(4.5)HP < X < 4(4.5)HP.
BTW, this leaves him vulnerable to a crit from an average weapon, but even that will not be guaranteed to kill him.
Or to put it differently,:
Assuming an average weapon does 1d8 damage x2 crit, the Fighter L1 has X HP, where 3(4.5)HP < X < 4(4.5)HP.
BTW, this leaves him vulnerable to a crit from an average weapon, but even that will not be guaranteed to kill him.