Tom Brady once quipped he'd retire when he started to suck. After last night's performance on Monday Night Football, many football fans are wondering if that time has come. 

Specifically, the New England Patriots lost 41-14 to the Kansas City Chiefs. The 37-year-old quarterback threw two interceptions and led the Patriots offense to only seven points. (His backup, rookie Jimmy Garoppolo, produced the other touchdown, when the game was out of hand.) For Brady, it was another poor showing in the young season. After four games, his passing stats are among the worst of his career. For example, his 5.77 yards per attempt are almost two yards below his 7.4 career average, notes the Boston Globe. 

More than this, the Patriots are 2-2. Such an average record is hardly a catastrophe by NFL standards. But by the standards of Brady's Patriots--who've appeared in three straight AFC championship games, and who won three titles in four seasons at the start of the millennium--the choppy beginning is cause for alarm. It's even cause to ask what for the previous 14 years has been an unthinkable question: Is Brady finished?

As a longtime football junkie and business writer, I have two answers to that question. The football junkie says Brady is on the proverbial back nine. I've watched him closely since his second season, and I've never seen him miss so many open receivers. Even when he has time to throw, he is inaccurate. Last night he threw like a quarterback with little confidence in his teammates, his coaches, or himself. 

But the business writer in me says it's impossible to judge Brady's performance in a single-game vacuum. His poor performance is, in fact, a reflection of the poor talent surrounding him. It's also a reflection of the Patriots culture, which has proven, time and again, that it seldom retains or properly compensates accomplished veterans. I don't say this like it's an altogether bad thing. As the scoreboard indicates, the Patriots' trim-the-fat approach has led them to three straight AFC title games. 

Regardless, there was something unsettling about Brady's uncharacteristically poor play on Monday night. Why, then, should football fans refrain from using last night's game as a key data point in evaluating Brady? First of all, what makes football a special sport--both in college and in the pros--is that there are so few games each season. Every Saturday or Sunday feels like an event or a cherished holiday, more precious for its scarcity. To be a fan is the feel the temptation to render judgment on teams and players based on how they perform on these sacred-seeming occasions.

But in the same way you can't judge your relatives--not entirely, at least--by how they appear on one stress-filled day a year, it's likewise misleading to evalutate players on a single-game basis. Sure, there's a lot you can glean from lone games: speed, effort, toughness, instincts, and decision-making. I'm not suggesting football fans stop observing and judging. Making those snap judgments--and making them accurately--is one of the joys of watching sports. But I'm suggesting, too, that it can be wise to draw a line between single-game feedback and overall performance evaluation. 

Ethan Bernstein, an assistant professor of business administration in the organizational behavior unit at Harvard Business School, recently cited the ability of legendary soccer coach Sir Alex Ferguson to draw this line. Ferguson, the former manager of the Manchester United club, championed the use of vests fitted with GPS sensors on his players during practice. The sensors, Bernstein writes in the Harvard Business Review, have allowed Ferguson to analyze his players' practice tendencies.

Yet in spite of his access to this data, Ferguson has said that he would "never criticize a player during a training session. That's where they try the irreverent things that will, and won't, work during a match." 

To be sure, part of Ferguson's point is one legendary basketball player Allen Iverson made famous: Don't evaluate practice as if it's a game. But there's another key piece of it, one to which all leaders, managers, and sports fans should pay attention: Even if you have the data on which to base an evaluation, you should still use discretion about how and when to deliver that evaluation.

Think about it: If Ferguson stopped each practice to critique his players for every single act of inefficiency, they'd probably stop experimenting. They'd also probably stop having fun. So would your employees, if they felt like every public minute of their day were a data point for a future managerial evaluation.

"There are all these breadcrumbs we leave digitally around the work place these days," says Bernstein, with whom I spoke this morning. "Collecting them can seem like a good goal, toward making the workplace meritocratic. But it may be hurting productivity. No one wants to feel constantly measured and evaluated." 

That's true for football players too. Even for legends like Brady.