Back Hopping (Accelerated Back Hopping (ABH)) is the main method of movement for speedrunning on OrangeBox Engine-based games. After ABHing was patched in a Gmod update due to it being a glitch in the OrangeBox Engine, It was reimplemented back in to NGS via the Backhopping Unfix addon on the Steam workshop.

1. Jump forward,
2. Turn around while you're in the air,
3. Right when you land, jump again and hold A or D.

Tips:

• Don’t hold the forward or backward keys (usually W or S) while doing this.
• It's much easier if you bind jump to your mouse wheel. (bind mwheelup +jump; bind mwheeldown +jump; bind space +jump)

Video Tutorial

How To Perform

1. Start with an ABH, like you normally would.
2. Instead of turning all the way around in the air, just slightly turn your view to the left or right.
3. Then, hold S + D (if you turned left) or S + A (if you turned right).

Video Tutorial Accelerated Side Hopping (ASH)

How To Perform

• Start by jumping and moving forward (normal W + jump).
• Turn around 180° in the air so your character is moving backward.

As you land:

• Tap S (backward) at the exact moment you jump again.
• Repeat the jump + S-tap rhythm to maintain and build speed.

Video Tutorial Check Out +strafe Method Accelerated Forward Hopping (AFH)

• Accelerated Back Hopping (Easy)
• Accelerated Side Hopping (Skilled)
• Accelerated Forward Hopping (Highly Trained Professional)

Source: https://wiki.sourceruns.org/wiki/Accelerated_Back_Hopping