My university experience is from a real long time ago and may no longer be relevant to contemporary education, but here goes:
Most of the introductory “100 level” courses were taught by professors talking in front of a large lecture hall with one to two hundred students. Then once or twice a week, there would be a “discussion section” where the class was split into small groups that met with a graduate teaching assistant (TA) to ask questions and turn in or receive back assignments. (This wasn’t true in all disciplines.) Unless your name was in the headlines of the sports section, there is no way the professor would know you were an athlete. In fact, except for a small cohort that hung around during his office hours, he would be very unlikely to know who most of his students were.
As to being a freshman, introductory courses had a good mixture of people from all four years. Freshmen might be a majority, but there were sophomores and juniors who couldn’t decide on a major and stick to it, and an introductory science course might even have senior humanities majors who were finally getting around to completing their science requirement (or vice versa). Even though the class list had your year on it, it made no difference.
In fact, it wasn’t even unusual for freshmen to be in a more advanced course. For example, if you had four years of the same foreign language in high school, you could take a placement test and find yourself in the junior-level class. And they gave a placement test to see if math students could start in pre-algebra, introductory algebra, introductory calculus, or skip those altogether.
Professors at my college just didn’t care about those things. They gave the top grades to the top students and the low grades to the poorer students. They were happy to encourage students who did well or were trying and happy to discourage students who didn’t try or clearly had no aptitude for the subject.
As a graduate student, I spent a couple of years as a TA in introductory courses (that I never took myself). It was a great experience. Each professor decided his grading scheme on his own, but all of the professors I worked for used pretty much the scheme: Add up the test scores and set a cutoff level for A, B, C, etc.
If a student was within a few points of a higher grade, ask the TA if they had any input and sometimes make an exception.