How to explain missing grade on transcript I am an undergraduate mathematics student in the United States. I'm applying to many REUs in a certain topic. My only coursework in this topic is a graduate-level course I took last year. However, for some reason, none of the students in the class have received a grade. The professor who taught it has a history of turning in grades long past the deadline, and it's very difficult to get her to submit even after consistent reminders (this is the first time it's run this close to the deadlines). 

Suffice it to say that the missing grade is not due to a poor performance or incomplete coursework (as far as I know), but just because the professor hasn't graded the final exam yet. Chances are the grade will not be posted before REU applications are due. 

So, what is the best way to explain the blank spot on the transcript in my REU applications without sounding accusatory or sketchy? I feel like blank grades have a hint of "plagiarism/cheating investigation pending" or "incomplete coursework" that could tank my application if I do not explain it correctly and in a place that is easily noticed by application readers.
If the suggestion of Andreas Blass doesn't work for you, then include a note somewhere saying that the professor is late in assigning grades to the class as a whole and that questions about that should be directed to the chair or the dean. Give an email address for that person as well as the name. 

You don't need to accuse the professor of anything and there are several valid reasons for grades being late, whether they apply here or not. But the administration can verify your claims and should be willing to do so. 

Just state the facts and point to an authority who can verify them.