Wiktionary
vb. (present participle of slap down English)
Usage examples of "slapping down".
The whine of the gearboxes grew in pitch and the tank lurched ahead as the clutches engaged, the heavy tracks slapping down on the solid rock of the Road.
She would assume he had been with Bill or Richie or 'the Jewboy,' as she called Stan (insisting that she meant no prejudice by so calling him, but was simply 'slapping down the cards' - her phrase for truth-telling in difficult situations).
He was only a kid, still wet behind the ears (as his mother sometimes told him when she was 'slapping down the cards'), but even a kid of eleven knew that you didn't give someone real medicine and then write on the label Administer as needed.
Such as not slapping down a tipped turbolaser like Kyp Durron the minute he started showing dark side tendencies of his own.