A trendline breakdown occurs when the price decisively moves below an important rising trendline that has been acting as support. It indicates that buyers are losing control and selling pressure is increasing. A strong bearish candle closing below the trendline, preferably with higher volume, gives stronger confirmation. After the breakdown, the previous trendline support can sometimes turn into resistance during a retest. If price fails to reclaim the trendline and continues making lower highs and lower lows, the bearish structure becomes stronger. However, a quick move back above the trendline can indicate a false breakdown.
In simple terms:
Rising trendline support → breakdown → retest → rejection → bearish continuation.