The Muay Thai side kick is a hybrid between the traditional teep and a taekwondo-style side kick. It carries more power and range than a standard lead teep, and it's harder to catch because of the foot position at impact.
Here's what makes it work.
All your weight goes onto the back foot BEFORE you initiate. You slide forward -- not hop, not jump. Sliding is faster, more powerful, and harder to read.
As you extend the kick, your hip and shoulder rotate completely so you're side-on to your opponent at the point of impact. This rotation is what gives the Muay Thai side kick its extra range over a standard teep. It also turns the bottom of your foot toward the target instead of the ball of your foot, which changes the striking surface entirely.
Lean back slightly as the leg extends. This keeps your weight posted on that back leg so you don't fall forward after contact. If you're lunging into the kick, you've already lost your balance and your next move.
The side kick works both offensively and defensively. Moving forward, it's a range-closing weapon that pushes your opponent back and creates openings for follow-up strikes. Moving backward, it disrupts their rhythm as they try to close distance on you.
Most fighters never develop this kick because they default to the round kick for everything. That's a mistake. The side kick attacks a different angle, targets the midsection with a pushing force, and keeps aggressive opponents honest.
For the complete breakdown of every kick in Muay Thai, check out our full guide to types of kicks in martial arts. Get the full course in the Ultimate Muay Thai Training System.