It might be against the terms of service of the website you're crawling, which puts you in violation of the Computer Fraud and Abuse Act (i.e. you're considered to be "hacking" them).
Well however you classify it doesn't matter, what matters is how the government classifies it. There's the tragic story of Aaron Swartz who was caught up in this non-sense: https://en.wikipedia.org/wiki/Aaron_Swartz.