Is the puck is something that you must watch at all times a run on sentence

According to the given sentence The puck is something that you must watch at all times. "Is not a example of a run on sentence." A run on sentence is two sentences that are best fit being one sentence instead of two. For example My cats name is Fred. He is really fluffy. would be a example of a run on sentence because the two sentences are best fit being one so it should be My cats name is Fred he is really fluffy.

Hope this helps.

the verbal in this sentence is an infinitive. when you want to know the reason of an action, you simply ask the question "why? ". once you know the reason you can answer with "because".

many times we don´t use the word "because" but we can use another expression and that is an "infinitive of purpose". example:

-why did your brother bring a book?

-he brought a book to study.

in the answer above you can see an example of an infinitive sentence, just like in the example of your text. "he couldn´t run fast enough to beat his older sister". so, the answer is infinitive.