Buff

Intercept

The Intercept buff will block any attempt to place a crowd control debuff on a Champion, even if it is specified in the enemy's skill that the debuff itself cannot be blocked. This includes Stun, Sleep, Freeze, Provoke, Fear, True Fear, Petrification, and Sheep debuffs.
A Champion can receive multiple stacks of the Intercept buff. Each Intercept stack will block one attempt at placing a crowd control debuff. After the attempt, one Intercept stack will be removed. The Intercept buff has no duration, and therefore cannot have its duration increased or decreased. The Intercept buff also cannot be spread to ally Champions.
If a crowd control debuff is placed on a Champion that has an Intercept stack and the Block Debuffs buff, an Intercept stack will not be removed. However, if a crowd control debuff that cannot be blocked is placed on a Champion with both Intercept and Block Debuffs, an Intercept stack will be removed.
If a crowd control debuff that can be blocked is placed on a Champion who is immune to that debuff, an Intercept stack won't be removed. However, if a crowd control debuff that cannot be blocked is placed on a Champion who is immune to that debuff, an Intercept stack will be removed.
If a Champion is under an Intercept buff, and another Intercept buff with less stacks than the Champion currently has is placed on them, the number of Intercept stacks on the Champion remains unchanged.
If a Champion steals an Intercept buff from an enemy, they will also steal as many Intercept stacks as the initial Champion had when the buff was stolen.
What the game's own status effects screen says

In the game data this effect appears as Negator.

Champions that apply it

7 champions have a skill that applies Intercept, according to the effect lines in the game data. This lists who applies it, not how reliably: chance, duration and resistance are on each champion's page.

The description is the game's own text. It has not been tested in battle here, and the game's wording can be loose (for example about numbers that differ between versions of an effect). See Data quality for what has and has not been checked. Found a mistake? Use "Report a problem" at the bottom of the page.