Trend line break:
Usually price respect trend line and it repels trend line every time and touch and repels but certain situation where trend line breaks occur. specially Economic events or news release, NFP , other special news events . News acts as trigger for breaking trend line. At that time price breaks trend line and new trend start in respect of that time.
Read More :- http://xpert-forex.blogspot.in/2012/10/day-trading-trend-line-strategy.html