You would use it: "I pummeled him to the ground." Meaning you ran into him with a lot of force/forcefully shoved that person to the ground. Or you can just run into that person forcefully, thus pummeling them.
When it has a subject, verb, punctuation, capitalization, a predicate, and a complete thought. A sentence is a sentence when it is handed down by a judge (or a magistrate).
No, it is a proper sentence. The subject is 'You', the verb is 'overflowed', and 'it' is the object of the sentence. All it needs is a period at the end.