Why in god's name would you choose to put it down a leg‽ That shit will give you the worst rug burn imagineable if you happen to take your pants off too fast or fall in a split or just sit down on your pants in a weird way where they pull against you if you try to shift in the wrong way.
Well my non-circumsized penis hangs out in my left pant leg and even without underwear, I've never had chaffing as an issue.
Have you? Have you even an uncircumsized dick? Because, how would you know if you don't?
The only time that's been even slightly an issue is when putting on pants without underwear just after sex, putting on jeans without underwear and while the foreskin was behind the glans and not on it. Which is when I'll just grab my junk, roll the hood back down to cover most of the glans and then no chaffing.
And if you don't put your dick in your leg, where else would you?