NavMeshAgent Collision

You will want to use OnCollisionEnter in conjunction with object tags. Tag the NavMeshAgents with a specific tag that indicates they are an Agent. Place the below function inside of the Player's class and when he collides with an object, it will check if the object has the NavAgent tag and if it does you can do some reaction.

 OnCollisionEnter(Collision otherObject)
 {
    if(otherObject.gameObject.tag == "NavAgent")
    {
       // Reaction
    }
 }

Reference Links

http://docs.unity3d.com/Documentation/ScriptReference/Collider.OnCollisionEnter.html http://docs.unity3d.com/Documentation/ScriptReference/GameObject-tag.html