Here's my two cents. I think everyone else has said the really important stuff, and I loved what AnimEdge said about control and beserk. It was said, a little more poetically, in Ender's Game: "Ender's anger was cold, and he could use it. Bonzo's was hot, and so it used him."
I would make sure that they were going to throw a punch before I did anything. That dosen't mean they have to land it. If not for ethical reasons, then legal reasons. Then probably a blood choke, depending on how much I don't like them. Or maybe a suitcase hold, or a gate punch, or a spiral lock, ... so many options. :uhyeah:
I think it takes a while to get used to adrenaline, so try two things before a sparring match. Smile and think "happy" thoughts. Smiling confuses people, plus it makes them think you know something they don't, or that you're crazy. Thinking "happy" thoughts releases go instead of adrenaline. Very similar but a little different. On top of that it helps you keep a level head.
Last thing (this post) "Every situation is a multiple opponent situation, unless proven otherwise." Or so I'm told. Keep your eyes open.
I apologize for any preachy-ness in this post, forgive me, I'm young.