# Matter Physics - custom filter before collisionstart / collisionactive to prevent this events

**URL:** <https://phaser.discourse.group/t/matter-physics-custom-filter-before-collisionstart-collisionactive-to-prevent-this-events/9625>\
**Category:** Phaser 3\
**Created:** [May 19, 2021, 10:00am UTC](https://phaser.discourse.group/t/matter-physics-custom-filter-before-collisionstart-collisionactive-to-prevent-this-events/9625 "2021-05-19T10:00:12Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![Puccini](https://yyz2.discourse-cdn.com/free1/user_avatar/phaser.discourse.group/puccini/32/4984_2.png) [@Puccini](https://phaser.discourse.group/u/Puccini)\
**Post date:** [May 19, 2021, 10:00am UTC](https://phaser.discourse.group/t/matter-physics-custom-filter-before-collisionstart-collisionactive-to-prevent-this-events/9625/1 "2021-05-19T10:00:12Z")

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Hi there,

i’m using the events “collisionactive” / “collisionstart” to check, what is happening in my scene and should i update some object values…  
I’m using the “setCollisionCategory” and “setCollisionGroup” to group my players, objects and bullets.

But:  
if a player fires a bullet, he can be hit by his own bullet and this stops the bullet from flying.

i need some filter option before the events fire like (psydo code):  
`if( bullet.player == collisionpartner.id ) return false;`

Is there any option?  
Thx a lot!