officiating

Question
We attempted a onside kick and one of our players was offsides.  The referee blew the whistle to blow the play dead.  Nobody could hear the whistle because of crowd noise or whatever and the player who was offsides was the first to the ball.  Our oppenents caught the ball on the bounce and was tackled by our player.  We received a dead ball unsportsmanlike penalty on the play.  I was under the assumption that it was a loose ball and shouldn't have been blown dead. Then the receiving team would get their choice of the play or kick over, plus the penalty for offsides. Thus we wouldn't have received the unsportsmanlike penalty

Answer
David
Thank you for your question.  To better understand your quest I need to know what rules you were playing under Federation or NCAA.  I assume Federation.  Secondly, I need to know if the deadfall could was really unsportsmanlike conduct or was it a personal foul.

Based on your question the official blew his whistle when the kicking team player was off side - under federation rules this is a dead ball foul and at that point it is a 5 yard dead ball foul against the kicking team.  The ball is dead when the encroachment/off side occurs so the kicking team must avoid contacting the receiving team. Under NCAA rules it would be a live ball foul, but since the official blew the whistle the ball is dead and if played under NCAA rules there may be an inadvertent whistle during a loose ball play. But the enforcement spot would be previous spot.

Now you said there was an unsportsmanlike foul.  If the foul was for the tackling or contact with the receiving team during the dead ball that sounds like a dead ball personal foul.  Based on the assumptions that this is a game played under Federation rules the enforcement spot should have been the previous spot.