Grappling and shoving are special melee attacks that require the Attack action (PH, 195). An opportunity attack is a special reaction. Take the Ready action if you want to attempt a grapple or a shove as a reaction.
and his ramblings
Grappling and shoving are special melee attacks that require the Attack action (PH, 195). An opportunity attack is a special reaction. Take the Ready action if you want to attempt a grapple or a shove as a reaction.