hard knocks

NOUN
11 LETTERS · STARTS WITH H

hard knocks is a valid 11-letter word worth 24 points in Scrabble and 25 points in Words with Friends.

SCRABBLE WORDS WITH FRIENDS
H4A1R1D2K5N1O1C3K5S1
4 + 1 + 1 + 2 + 0 + 5 + 1 + 1 + 3 + 5 + 1 =24 PTS
DOUBLE WORD → 48TRIPLE WORD → 72
MEANING

What does hard knocks mean?