To Throw Against
To Throw At
transitive verb, ichidan verb
You know that you're throwing something that is attaching to something else. How else can you say that? The best way would be to say to throw against or to throw at.
The readings just come from two vocab words you've hopefully seen already: 投げる and 付ける. So long as you know the readings for those words, the reading for this word should be no problem for you.
It's rude to throw pebbles at people!
My father got angry and threw a balloon at my mother.
The prince tried to throw an onion at the vampire for the time being.