The phrase "title defense" means protecting or fighting to keep a championship or title that someone has already won against challengers or opponents who want to take it away. Full definition
The defending champ is starting to get some cushion with a little more than 18 holes left in his Masters title defense. (sbnation.com)
Let's all just ignore my performance, totally normal title defense going on here. (theshortfuse.sbnation.com)
Joe Brown, maturing lightweight world champion, called on experience of 32 - odd years to outpoint 26 - year - old southpaw Kenny Lane, eke out fifth title defense in 23 months. (si.com)