My husband & I were sitting outside with our 7.5 month old male. He is not neutered. Lucas is well socialized & has a great trainer & he never behaved aggressively before so we were both puzzled as to why he decided to suddenly lunge & bark at a man that walked across our sidewalk. It was in the evening & the man walked very close behind my husbands chair on the way by. Lucas was in a sit stay at the time but jumped up & lunged. He was leashed so he didn't bite or make contact with the man. He didn't snap but it was a very loud, deep bark. What's going on with him? It's only been once but I want to make sure I address it immediately. Any thoughts on what would make him do this? Is it his age?