Accelerated Back Hopping (ABH) is a movement exploit in Source-based games (like those on the OrangeBox Engine) that allows players to rapidly accelerate backward. It became a staple for speedrunners due to its ability to drastically increase movement speed. While ABH was patched out in later versions (such as in Garry's Mod), it can be restored in NGS using the Backhopping Unfix addon.

1. Jump forward.
2. While in the air, turn around.
3. As you land, immediately 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