Never use the rudder on takeoff ??????? You almost have to, to counter the tendency of the prop wash pushing the tail over.(P-factor)
There is another possibility.....You're setting up the tail wheel before you fly.....then you trim rudder and throw the tail wheel off......or the main wheels are crooked a tad and the tail wheel keeps you straight until on takeoff roll the tail lifts and you're back on the mains......But rudder is a must on takeoff