There is an unspoken agreement, particularly in the time before the widespread use of batting helmets, that fast bowlers will not bowl bouncers at each other, because less skilled batsmen are less likely to effectively defend and therefore more likely to be struck. Breaking of this rule can lead to "bouncer wars" – that is, the targeted bowler engaging in retaliatory hostile short-pitched bowling at his opponent during the following innings. Because of the potential danger to batsmen of being hit and to stop bowlers bowling bouncers all the time, there are Laws in the Laws of Cricket governing how frequently a bowler may bowl bouncers, as well as how many fielders may field backward of square leg. These laws take into account the relative skill of the batsmen. During the 1970s to 1980s, bouncers were used as part of a team's intimidatory tactics, especially by the West Indies team. In 1991, the International Cricket Council (ICC) introduced a "one bouncer per batsman per over" rule in an attempt to discourage use of intimidation. However, the ruling was not well received by players and umpires alike, with English umpire Dickie Bird describing it as "farcical" as he felt that calling intimidatory tactics should be left to the umpire. The ICC changed it to two bouncers per over in 1994, with a two-run no-ball penalty (rather than one-run no-ball) if the bowler exceeded two bouncers an over. One Day International cricket allowed one bouncer per over in 2001 (and a one-run no-ball in case a bowler exceeded the limit). On 29 October 2012 the ICC increased the number of bouncers that could be bowled during a One Day International to two per over. The number of bouncers per over allowed in T20s was kept to one. Fast leg theory, the deliberate and sustained bowling of bouncers aimed at the body, coupled with a cordon of legside catching fieldsmen to catch deflections, was a tactic used by England against Australia in 1932/33, dubbed the Bodyline series by the Australians. This controversial tactic caused the Laws of Cricket to be reformed to prevent any recurrence. In 1954–55 in Sydney, England fast bowler Frank Tyson bowled bouncers at Australian Ray Lindwall, who returned the favour by hospitalising Tyson with one of his own. An angry Tyson returned with a large lump on his head and took 6/85 in the second innings to give England a 38-run victory.