combative
adj.having a tendency to argue or fight. You use this to describe someone who is always ready to challenge others or disagree with them.
adj.characterised by a tendency to argue, fight, or challenge others. Often used to describe a person's personality or a specific style of debate.
“He has a combative nature and rarely agrees with anyone.”
“The politician's combative style made it difficult for her to find common ground with the opposition during the debate.”
“The legal team adopted a combative approach to the settlement, refusing to compromise on any of the core terms until the final hour of the trial.”
“The spokesperson has been known for his combative approach with the media and fervent defence of the president.”
“Helpfully, his ballplaying ability is matched by some equally impressive – and combative – defending.”
From combat + -ive.
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.