Under the Awesome Blow Barbarian ability, on a Failure it says "You gain the normal effect of Knockback." I can't find it in the status effects at the end or on the GM's screen. Is it hidden away somewhere? Is it a mistake and they actually meant "Shove" on pg. 243? That's my best guess.
That's not the only way to knock back smaller foes. It's just that hard for PC races to gain.
Ex. Stone Giants (only level 8) have Big Swing which knocks you 10' (20' on crit) which can be useful since they live in mountainous territory...with cliffs.