daf bit: Eruvin 48

As previously discussed, under some circumstances on Shabbat you can be limited to a range of only four cubits. Why four cubits? Because it says "every man abide in his place" (Ex. 16:29), and "his place" is understood to be three cubits for his body and one for stretching. R. Mesharsheya asked his son to ask R. Papa: are these four cubits measured by each individual's arm, or by the standard measure? If by the standard measure, then what does Og, king of Bashan (who is a giant) do? And if it's each individual, why hasn't this been taught as such? R. Papa answered: it is calculated by the arm of each individual, but the ruling could not be definite because a person might have stumped limbs (and we want to apply the standard measure in that case). (48a)

Why Og, an Amorite king (and thus, presumably, not Jewish) would be concerned about Shabbat restrictions is not addressed here. Presumably he's just an example, or they consider it in case he converts.