For most players that play USTA League, their high and low match rating during a year are typically about 0.4-0.5 apart. For example a upper half 4.0 (a rating around 3.80) will likely have some match ratings just over 4.0 and others down around 3.5. This happens naturally just due to good/bad days or good/bad match-ups or variations in how partners play etc.
But to ATP pros have the same variation? Or do they even have more?
The charts I included in my comparison of some of Novak's and Federer's best seasons actually shows this fairly well.
In 2011, one of Novak's best years, he had a high match rating of 7.39 in the Australian Open final and a 7.31 in the US Open final, but he had some stinkers too. He had a few 6.85's in closer than expected wins in the first half of the year, but then lost to Ferrer and Tipsarevic at the Tour Finals getting a 6.53 and 6.71. That is a 0.86 difference from high to low! Now, perhaps Novak just ran out of gas at the end of the year, but you can see the effect of that in the chart below.
Federer had one of his best years in 2004 and had a 7.34 against Hewitt at Wimbledon and a 7.42 against him at the US Open. But he also had a 6.56 in a loss to Costa in Rome and a 6.66 in a loss to Kuerten at the French. These were on clay against clay court specialists so perhaps that explains the 0.86 difference, but he also had a 6.71 in a loss to Hrbaty in Cincinnati, one of his favorite tournaments. And you can see quite a few lower rated matches in the chart below.
What about Nadal? He's had a few unexpected losses, the loss to Rosol in 2012 at Wimbledon garnered a 6.69 only weeks after a 7.49 in the French Open semi-final. In 2013 he went from a 7.38 in the French final against Ferrer to a 6.67 losing to Darcis at Wimbledon. He also had a 6.63 against Del Potro in Shanghai later in the year. Then in 2015, while he did not have the highs he'd had in prior years, a 7.02 at the French against Sock the highest, he had numerous lows including a 6.33 t Berrer in Doha, a 6.46 losing to Berdych in Australia, a 6.44 losing to Dolgopolov in London, and a 6.50 losing to Dustin Brown at Wimbledon.
Andy Murray is not immune from this either. In 2013 when he won Wimbledon with a 7.17 beating Novak, he had a 6.45 against Mahut at Queens Club, a 6.51 in Monte Carlo, and a 6.53 at the US Open, the last two against Wawrinka.
A common theme in the lower rated matches is playing at tournaments or on surfaces that aren't the player's best, or when changing surfaces, but in some cases also playing a player that is a bad match-up for them or at a time when they are tired or fatigued. This is exactly what happens with us in USTA League play too. There are facilities or courts that we don't like, bad match-ups, being tired, etc. The top pros are not immune from this and have bad matches too.
So take heart, if you have a bad match, you can rebound too and play well in your next one.
Attribution: Match data is courtesy Jeff Sackmann / Tennis Abstract.