The problem is that it doesn't look like he thrust the spear, more like he just extends his arm like he wants to push something over.
So firstly that means you have to remove some frames before the attack. What is also very important is an anticipation frame,
your animation already kind of had this, but it didn't really work out well since he never returns his spear. Then you can also add a cool effect where you have 1 frame where the spear goes further than it should go, this makes it look a lot more lively and active.
Example:
If you wanna be a really cool dude you can add a SMEAR. this might not always work so be careful when you apply it, but I think it works here.
Example:
Here is a picture of both spritesheets:
Hope this helps a bit.