The most common and most likely answer to this crossword clue is the 3 plus 4 letter word OWN GOAL
I've seen this crossword clue in The Guardian
O
W
N
G
O
A
L
More clues leading to the result OWN GOAL
- Personal target leading to footballer’s error
- Bad mistake to have ambition
- Go on law breaking in self-defeating act
- Take responsibility for a design blunder
- Defender’s regret, perhaps, to have ambition
- Defensive error gets cry of pain, followed by a long analysis
- To have ambition is a self-inflicted disadvantage
- Admit ambition’s a mistake
- Error that hurt Logan, unfortunately
- Keep end in Pyrrhic victory, say
Buddy explains!

The straight part
We know that "a self-inflicted disadvantage" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case a self-inflicted disadvantage = own goal.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.