Tapping-up is something that seems to go on a lot more frequently these days, but it still remains as illegal as ever.
The rule regarding this dark art (via the Mirror) can be defined as: "Subject to Rule T.7, a Contract Player, either by himself or by any person on his behalf, shall not either directly or indirectly make any such approach as is referred to in Rule T.5 without having obtained the prior written consent of his Club."
Down the years, clubs have tried to go about this business in all sorts of sneaky ways, but there have been some high profile cases that ended up a bit messy.
6. Paul Pogba - Le Havre to Manchester United
Long before signing Paul Pogba in a sensational £89m move in 2016, Manchester United poached the promising young Frenchman from the youth setup at French club Le Havre.
Following on from another high profile case in 2009 further down this list, United stood accused of trying to entice Pogba into breaking his contract and joining up with the Red Devils for big wages for his age.
Le Havre put out a statement on their website with their version of events, which United refuted and threatened to sue over. They were then cleared over any wrongdoing but the decision wasn't recognised by Ligue 2.
5. Christian Ziege - Middlesbrough to Liverpool
German star Christian Ziege's case resulted in record financial punishment in 2000, after he transferred from Middlesbrough to Liverpool.
The summer was spent by the Reds easing the player's fears about game time and massaging his ego, before a secret clause was triggered to the tune of £5.5m
Liverpool were found guilty of inducing Ziege to breach his contract, and were hit with a £20,000 fine, with Ziege himself having to fork out £10,000 for his own role in the situation. He became a hate figure in the north east for his troubles, and has since admitted he regrets the cloak-and-dagger nature of the move.
4. Academy Starlets - Manchester City & Liverpool
In 2017, both Manchester City and Liverpool were found guilty of tapping-up youth players from various academies that weren't there own, using bribe tactics.
The Reds offered a 12-year-old boy from Stoke's youth setup bribes to sign for them, as was his family. Man City attempted to sign an 11-year-old from Everton and a 15-year-old from Wolves for their academy.
Both sides were found guilty of using illegal methods and both received two-year bans from signing registered youngsters.
3. Robbie Keane - Tottenham to Liverpool
Self-confessed Liverpool fan Robbie Keane was at the heart of an illegal approach made by the Reds in 2008.
The Irishman moved to Anfield from Tottenham but incensed chairman Daniel Levy after it came to light that he had been tapped-up in an unauthorised approach.
Liverpool were not fined or docked points for their pursuit of Keane, but did sour their relationship with Spurs and no transfers have been facilitated between the clubs since.
Keane fared poorly in his one and only season on Merseyside, and re-joined the Lilywhites with his tail between his legs.
2. Ashley Cole - Arsenal to Chelsea
Ashley Cole's transfer to Chelsea from Arsenal in 2005 was far from straightforward.
The left-back was found in breach of rule K5 which forbade him from speaking to Chelsea about a possible move to the Blues without the permission of the Gunners.
Cole was actually spotted meeting then-manager Jose Mourinho and Peter Kenyon at the Royal Park Hotel in central London to conduct secret business. Chelsea, knowing they were playing with fire, broke rule K3 which prevented them from approaching Cole whilst he had two more years left on his deal.
Mourinho was also in trouble for his role in governing managers' conduct (rule Q). In conclusion, Cole was fined £100,000, Chelsea £300,000 and a suspended three-point deduction, and Mourinho £200,000. Cole's agent received an 18-month suspension.
1. Gael Kakuta - RC Lens to Chelsea
In 2009, the dark art of 'tapping-up' really came to the forefront, with the case of Gael Kakuta one of the biggest controversies at the time.
The French youngster's club RC Lens reported Chelsea over an illegal approach, which resulted in the Blues getting hit with a transfer ban until January 2011. The club also had to pay €130,000 to Lens in compensation, and the player himself had to fork out €780,000 for the role he played in engineering the move.
But later, the Court of Arbitration for Sport lifted the ban after establishing that Kakuta's contract wasn't actually valid with Lens - and that the pre-contract with Chelsea had been signed by his mother.