Question

Are you allowed to head butt another player in the chest ? (IN SOCCER)

Answer 1

I found this although I am not a soccer player nor do I know all the rules.
http://www.helium.com/items/1917508-nhl-head-butting-rule

and this.
http://www.soccerdrillstips.com/rules/soccer-rules-and-regulations-fifa.html

Answer 2

Zidane of France got red-carded for doing it deliberately in the 2006 World Cup. Do you recall that incident?

http://www.youtube.com/watch?v=vF4iWIE77Ts

Another player, Etoo of Cameroon, was recently banned for three games for a similar incident.