Wiktionary
n. (context British of a rival football club English) Making an approach to a player, under contract to another club, in order to attempt to negotiate a transfer.
Wikipedia
In professional team sports, tapping up ( British English) or tampering ( American English) is an attempt to persuade a player contracted to one team to transfer to another team, without the knowledge or permission of the player's current team. This kind of approach is often made through the player's agent. It is expressly forbidden in many professional leagues, but is not illegal.
Usage examples of "tapping up".
Bill Koontz was sitting at the counter tapping up tostada crumbs with his middle finger and licking them off when Joe and his people walked in.
She heard the stepping of feet in time to the music, scuffing on the ground and tapping up the stairs and over the floorboards of the veranda, and cried greeting with the rest as Astrid and Eilir burst through the door and out into the open space, making someone taking a shortcut to the jakes dodge aside.
Nog stared at her for a half second before snapping his attention back to his screens, tapping up damage reports and checking their shields—.
He could picture Selznak tapping up the cobbles of Gosset's drive with fog issuing from his ears rather than from his pipe.
Maximillian's feet began to jitter against the dry ground, his booted heels tapping up and down in a rapid rhythm as he struggled to regain control of his body.
To have William name the card so openly -tapping up - was not what I needed right now.
A moment later they could hear her small feet tapping up the stairs.