Bonus points (specifically) and how to get them
After in game testing:
- Any extinguishing of a teammate by non-Medic action: via Jarate, Mad Milk, Dispenser, or air blast.
- Destroying sappers using the Homewrecker as Pyro
- Destroying sappers on friendly buildings other than your own as Engineer
- Killing a Medic actively healing an opposing player as Scout
- Stunning a player with Sandman is 1 bonus point. Moon-shot stuns (long distance) are worth 2 bonus points.
- Healing teammates with tossed Sandvich/edible. This is the act of them picking it up, you do not receive healing points.
- 2 Headshots with the Huntsman grants 1 bonus point as sniper.
If you have damage indication turned on (Advanced → Show damage as a number over players) you will know you gained a bonus point when a purple "+1" (or "+2") appears on the player or teammate that let you gain it.
All other points go towards their respective categories. Cart pushes are added to capture point totals. All backstab and headshot bonuses go to kills. All direct or indirect healing goes towards healing @ 1 per 600HP healed.
With the rate Valve adds user content to the game, I am unsure if any of the newer weapons grant bonus points upon successful use, but it appears that bonus points are essentially granted for selfless team-centric acts.
Bonus points in my experience tend to be points awarded for doing things that generally aren't considered to be related to the goal (capping the points, killing the enemy). My memory tells me that bonus points apply:
Pyro: Extinguish a teammate
Possibly air blasting an enemy off the map or into a hazard like a saw
Engineer: Extinguish a teammate with your dispenser
Sniper: Extinguish a teammate with jarate
Scout: Extinguish a teammate with mad milk