These are opposites, not variants: offence is attacking or the act of causing hurt; defence is protecting against it. The spelling is the second question — offence and defence are British, offense and defense American. American English also stresses the sports senses on the first syllable: OFF-ense, DEE-fense.
The core difference
They sit at opposite ends of the same encounter. Offence is the attacking side, or the act that causes harm or insult. Defence is the resisting side, or the means of protection.
- The team switched from defence to offence. — sport
- He took offence at the remark. — insult given and received
- A criminal offence. — a breach of the law
- The defence called its first witness. — law
The spelling split
The -ce endings are British and Commonwealth; the -se endings are American:
- British: offence, defence, pretence, licence (noun)
- American: offense, defense, pretense, license (both)
Note that the adjective is defensive on both sides of the Atlantic — the s appears there regardless, which is part of why the noun spelling feels unstable to British writers.
Offence has two lives
The legal and the emotional senses share a word but not a tone. "A minor offence" is a small crime; "no offence" is an apology for a remark. Both descend from the same Latin root meaning to strike against, which is also why offend covers annoying someone and breaking a rule.
The sports usage
In American sport, offense and defense are units of a team as well as phases of play, and both take first-syllable stress. British sport uses attack and defence for the same idea, which is why "the offense scored" reads as American to a British ear.
Frequently asked questions
Is it offence or offense?
Offence is British and Commonwealth; offense is American. Both are correct in their own variety — match your audience.
Why is it "defensive" and not "defencive"?
The adjective takes s in every variety of English. Only the noun splits between defence and defense.
Are offence and defence opposites?
Yes. Offence is attacking or causing hurt; defence is protecting against it. They are not spelling variants of one another.