This is yet another ridiculous term in Daniel Cassidy’s apology for a book, How The Irish Invented Slang. Cassidy claims that the verb ‘to spar’ in boxing comes from the Irish spairn, which means fight, contention, struggle. In order to believe this, the word spairn needs to have been borrowed into English as sparring and this would then have to have been shortened to spar by the process known as back formation. This is not the case. We find the verb as sparrit, sparres and sparred in Middle English, where it meant to thrust or strike rapidly.
In other words, yes, there is an appropriate word in Irish, spairn, but there is an even more appropriate word in English, sparren, which was already in use in colloquial English six hundred years ago.