<http://schema.org/keywords>
"nfl chop block chop blcok rule illegal block nfl crackback block nfl nfl rule changes nfl bans chop block football chop block chop block dangerous chop block injury"^^<http://www.w3.org/2001/XMLSchema#string>
<http://www.si.com/nfl/2016/02/29/nfl-competition-committee-could-ban-chop-block>