Partly updated for Enshrouded 1.0— 1.0: the unlock cost; the rest is pre-1.0 wiki data

Kick
When equipped with a Melee weapon you can perform a Kick by attacking while blocking. Kick deals little damage but hits the target with massive force to fill up the enemies Stun Bar and pushes them back. Stun Bar increase scales with Dexterity.
Stun time depends on the enemy's size. Overpower Attacking blocking enemies or parrying their attacks fills their Stun Bar until they become overpowered. Overpowered enemies are open for Merciless Attacks.
Where Kick sits on the 1.0 tree
In the Ranger area. The cheapest way in from a starting point buys 3 nodes for 5 points, this one included (one rank each).
Related Ranger skills
Same archetype — likely candidates to slot next to Kick in a build.
Airborne1pValues in the 1.0 files: 12% per rank, 3 ranks.
Arachnoid1pValues in the 1.0 files: 20% per rank, 3 ranks.
Backstab Mastery1pValues in the 1.0 files: 20% per rank, 3 ranks.
Blessed Arrows1pValues in the 1.0 files: 8 per rank, 3 ranks.
Counter Battery1pValues in the 1.0 files: 8% per rank, 3 ranks.
Dexterity1pIncreases your Dexterity attribute by 1 Increases Bow and Dagger damage by 5% per Attribute Point
Eagles Bane1pDamage against flying enemies increased by 30%.
Endurance1pIncreases your Endurance attribute by 1 Increases Stamina by 10 per Attribute Point
Sources: game files 1.0 + Keen Games 1.0 patch notes (changelog, combat changes) for the unlock cost; enshrouded.wiki.gg (pre-1.0) for the description and effects.