Bowling Night is one of 28 Achievements in The Respawnables.
The description says Kill 25 enemies using Hand grenades.
Note that only enemies in the Mission Mode count as enemies.
Enemies in Multiplayer do not count towards this Achievement.
Grenades from a Grenade launcher etc. won't count as hand grenades.
Special grenades won't count as hand grenades as well.
The reward for this achievement are 10 Score Points (when achieved during a match).
Tips & Tricks
You can also simply weaken the enemy by hitting them long enough and then throw a grenade at them, a good choice for a weapon is the Scoped Assault Rifle.
You can also target the most immobile bot, especially when they are camping, like Masked Viper. Although, you may want to shoot him quite a bit, just to reduce his health, as he is wearing health boosting gear. Rocket Crush may become another good target, but beware, as his weapon is not meant to be taken lightly.
The damage it inflicts is not fatal if the opponent has full health, heavily armored or not, so do not be surprised if the enemy survives your pre-emptive/desperate attack.
A detailed strategy about hand grenades can be found here.