Ellis Harrison struck a hat-trick inside seven first-half minutes and ended with four goals as Bristol Rovers thrashed Northampton 5-0 at The Memorial Stadium.Harrison's first three strikes came between the 17th and 24th minutes as Rovers brushed aside the visitors, who showed little appetite for the fight.Rovers had taken the lead after seven minutes with a well-struck right-foot shot from the edge of the penalty area by Billy Bodin, which gave visiting keeper Adam Smith no chance.Harrison headed his first from James Clarke's right-wing cross but needed the intervention of referee Gavin Ward, who overruled his assistant who had flagged for a non-existent offside.It was 3-0 to Rovers after 21 minutes as Chris Lines' corner was headed back across goal by Mark McChrystal and Harrison bundled the ball across the line from close range.Harrison completed his treble three minutes later when Lee Brown crossed from the left and the striker backheeled the ball into the net.The points were sealed when Harrison shot his fourth in the 54th minute.