Question About Deer Behavior

A bit of a break from what we usually post here at IBA...

Last night, I went out into my backyard at dusk. There stood a young buck almost identical to the one pictured at the left.

No matter how much I waved my arms, clapped my hands, and shouted, he did not flee or turn away.  On the contrary, he stood his ground and became aggressive in his stance.  The closer I got, the more he stamped his front legs and stared me down.

What was going on?  I've never seen a deer behave in that manner when it isn't rutting season.