Hi,
As I mentioned before I get a lot of phone calls from people who have mowed their lawn too early after installation and it dies off. But even after your lawn is established it is still important to take some care when mowing your lawn. For instance some grasses, like Wintergreen couch, can Scalp when mown too low. This means that a white scaring appears on your freshly mown lawn- Basically more than the leaf head has been taken off. Almost like braking your nail too far back on your fingertip. Level 3 on your mower is an ideal level to cut your grass at, but if it is really long, ideally (and I understand that not all of us have all the time in the world to donate to our lawns) mow it on a higher level one day and then 2 to 3 days later mow it lower again. Thia will cause the grass less stress.
As you can see it is not the end of the world, and your grass should come back from it, but it will leave it looking a little crew cut for a while.
And really what we all want is easy as possible lawns, to play and admire but not work all day on.
Yours in turf
Sare