Cause of ink leakage from ballpoint pen
b) In case from the back of the pen
b-1) In case air enters from the pen point
As in the illustration above, when you write with the tip of the pen pointing more than horizontal, air enters from the pen tip and ink falls. If you leave the pen in this state, air may enter further from the pen tip and ink may flow out at the end of the pen.
In the case of the knock type, as shown in the illustration above "Knock button is pushed out unnoticed", air enters due to the rotation of the ball of the pen tip, ink may flow out at the end of the pen.