The United States hosts Russia in the Davis Cup finals next week in Portland, Ore. After much negotiation between the Davis Cup governing body, the ITF and the USTA, the finals will incorporate a new rule: players will have an unlimited number of opportunities to challenge line calls through “Hawk-Eye,” or electronic replay.

Under the normal rules, players are allotted two challenges per set, with an additional one in case of a tie-break. Players only use up a challenge if they are found to be wrong; they may challenge however many times they wish as long as they are determined to be correct.

Hawk-Eye was implemented as an officiating aid following a number of bad line calls in the highly controversial 2004 U.S. Open match between Serena Williams and Jennifer Capriati. To justify the cost of such a system — which entered in the six-digits range — Hawk-Eye had to provide both sporting value and entertainment value. To satisfy the latter, it was implemented with guidelines similar to those under the NFL’s instant replay system.

There are obvious reasons for allotting only a limited number of challenges in both tennis and football. With only a few challenges per game, players or coaches must be extremely selective as to which calls they call into question. The calls usually end up being those late in the set on set point or mid-fourth quarter with a three-point deficit — amounting to quite a bit of a spectacle and quite a bit of entertainment for the spectators.

Additionally, the system must account for the fear that players would abuse an unlimited number of challenges, bringing every call into question and disrupting and delaying matches.

But this seems to be a much greater risk in football than it is in tennis. In football, the red flag brings the play “upstairs,” where an officiating crew and the head referee view the play from a number of different camera angles and, based on that, uphold or overturn the call on the field. In contrast, in tennis, the Hawk-Eye camera system projects the exact position of the ball as it hits the court onto a large screen, and, based on that, the umpire upholds or overturns the call on the court.

Not only does the Hawk-Eye system require significantly less time, it requires virtually no deliberation or judgment. Cameras indicate whether the ball was out or in; there are no ifs or buts about it.

Furthermore, the Hawk-Eye system has already been implemented once before, in the 2006 Davis Cup Finals. Players called an average of 3.6 challenges per set, little more than the 2+1 challenges per set they are allotted under the normal rules. This is not actually surprising: players often cannot see the far baseline to judge calls because they are often moving after shots or their lines of vision are blocked by the net. Tennis players are simply not inclined to challenge the vast majority of shots due to the very nature of the game.

Furthermore, there are a number of benefits to allowing unlimited challenges. Such a rule would prevent a situation in which a clearly incorrect call is made at a crucial point in a game, but a player cannot challenge the call because he has already used up his allotted challenges. It would also remove the pressure on players to decide when to use a challenge.

In the 2007 Masters Cup, for example, Roger Federer could have had double break point against David Ferrer in the opening game. At 15-30, he hit a forehand that just clipped the line, but was called out. He hesitated and eventually decided against a challenge because he had already used one earlier in the game and did not want to risk playing without any challenges.

Unlimited challenges, therefore, prevent bad calls from slipping through. It allows the Hawk-Eye system to do what it was intended to do — ensure correct calls and fair play.