Minecraft – How to make arrows disappear when hitting the ground and not players

First set up an objective tracking player death, similar to what I outlined in my answer here. For the following, I assume that this objective is named hasDied and there are two teams, red and blue.

Instead of the testfor command in that answer, you can use

/testfor @a[team=red,score_hasDied=0]

Invert the redstone output, so that it turns on when nobody is left alive in team red and continue from there. Do the same thing for the blue team.

If you are a developer you can look further into cancelling the OpenInventoryEvent, it would look something like this, with a little editing of course. Or you can look into premade code such as RegionInventoryBlocker.

    @EventHandler(priority = EventPriority.NORMAL)
public void onInventoryOpen(InventoryOpenEvent event)
{
    event.setCancelled(true);
}

If you are a regular user, you can use a plugin such as http://mods.curse.com/bukkit-plugins/minecraft/lobbytools to disable the movement of things around on your inventory, this should do the job. You can also look into many other plugins that do this job.

Other than that, there is no other known way to completely disable the inventory.