The most common and most likely answer to this crossword clue is the 3 plus 4 letter word OFF BASE
O
F
F
B
A
S
E
Buddy explains!
The straight part
We know that "Uncle Sam’s wrong" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case uncle sam’s wrong = off base.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does OFF BASE mean?
OFF BASE adjective- Alternative form of off base