Ok, this guy’s knocked out some teeth here:

Danny Granger, American professional basketball player for the NBA’s Indiana Pacers, famously knocked out his two front teeth in a victorious game against the Boston Celtics on 1 November 2008. You can say both of these:

  • He knocked out two teeth.
  • He knocked two teeth out.

But you can only say one of these:

  • He knocked out them.
  • He knocked them out.

Compare: “knock out” is a phrasal verb like:
put away (aufräumen), bring up (=mention), try out, give up, call up, rip off (=steal), think over, boss around (herumkomandieren), make up (=invent)
They all use the structure of “knock it out.”
There are lots of lists and exercises here. Try them out!

Contrast regular two part verbs:
fall for, bump into, get over, look at, go up, fall down…
Look at them!

Knock ‘em out