I'll just restate what I've learned.
If he's coming at you with all straights, you just need to move out of the line of attack. Here's a couple of good ways:
1. Circle away. Easy enough for a guy who's just blindly advancing. His options from there are to continue chasing you, gassing himself out, getting frustrated, or he can change his plan of attack.
2. Parry-pivot. Awesome move that we do all the time at the Boneyard and that I succesfully used against a competing boxer in sparring multiple times. There are two ways to do it. For the descriptions, assume that you're both standing with a left foot lead.
If he's advancing towards you...
Parry his right straight while slipping to the outside. While doing this, perform a basic 90 degree pivot on your left foot. Your line of sight should now be perpendicular to his; you're facing his right side.
If he's not advancing, or just not moving fast enough,
Just modify the move by taking a step to the outside of his right foot. Step with your left foot to the outside of his right foot, and now perform the same pivot step. It's the same concept as in wrestling, when you use a penetration step if you need to close distance, or a simple knee dip if he's moving towards you. In this case, he's not closing the distance for you, so you need to get deeper and then pivot.
In any case, you flank him. If you're just boxing, you can deliver a combination straight to his jaw (straight punches would be best), or smash his liver. Obviously with kicks, knees, and takedowns, you have even more options.
This technique seriously works. It sounds like a lot of motion, and it sounds like he'd just face you, but seriously, I catch people with this all the time. I sparred a boxer who was in training for a fight at TriStar Gym over the summer, and I evaded a big right straight with this move, and he would be WAY off balance and totally out of position.
3. Drop-step. Another technique at the Boneyard we use for guy using the straight blast. You shouldn't ever be backing straight up, but in this case, it's okay, because it's short and quick, and you shift to the offensive.
Here's how the move works: He's coming towards you, throwing straights. Take no more than two steps backwards, before shoving off of your front foot straight back, and landing on your rear foot. It's like a hop, but stay VERY close to the ground; your feet should slide against the floor. When you land, most, but not all, of your weight will be on your rear foot.
You've now created a gap between you and your opponent. Because he was moving forward while throwing punches, there's a really good chance that the unexpected gap took him out of position and off balance.
Immediately, the instant your weight lands on your rear foot, explode forwards again with a right straight. It wouldn't be a bad idea to drop down to the body with the right straight to the solar plexus, since he's throwing head punches. Just an extra measure of caution.
What you've done is one or more of the following:
-Took him off balance and out of position
-Colliding his forward motion with your explosive forward motion and the force of your punch. It's like a head on car collision with 16 ounce gloves.
-Created an opening, and exploded back in during the time between his punches.
It's called a drop step also because you drop a little bit when you slide back. Basically you coil your body up (slightly, don't exaggerate like a fancy kata or anything), and then explode forward while punching. Any strike becomes much harder when you couple it with forward momentum.
It also might not be a bad idea to get in really close and work the shoulder butt.
