Haman Finds Mordechai Teaching Kemitzah
Haman comes to lead Mordechai through the streets and finds him teaching his students the laws of kemitzah of the Omer, on the 16th of Nissan.
Haman went to call Mordechai to parade him through the streets as directed by Achashveirosh. Mordechai was studying with his students the laws of kemitza. Had the Beis Hamikdash been standing, the korban omer from newly grown barley would have been brought on the 16th of Nissan, the second day of Pesach. Kemitza is performed by a kohen who takes a handful of grain from the korban omer. Mordechai was specifically studying these laws with his students. Since they, unfortunately, could not bring the korban omer that day, they were studying its laws instead. (Rashi) This event, therefore, took place on the 16th of Nissan.