'hardly follow' is a correct and usable phrase in written English.
It is used to indicate that something is not very easy to understand or is too abstract for the speaker to grasp. For example, "I couldn't quite understand the professor's explanation of quantum mechanics - I could hardly follow what he was saying."
Students hardly follow Mill's curriculum — there is no Greek or Latin in kindergarten, or even in later grades.
I was so profoundly appalled by the bludgeoning of Jessica Alba, I could hardly follow the rest of the film.
Usually in German productions, you listen to a kind of poetic translation that sticks to the blank verse, but you can hardly follow the language because it can't capture the complex thoughts in Shakespeare's lines.
The prosecutor added: "We have over 130 who we know have come back from Syria, and spent a certain amount of time there, and we can hardly follow up on them.
Or is real life trickier?" So in The Long Goodbye, Elliott Gould delivers a brilliant performance as Philip Marlowe – cool, shambling, untidy and improv, dazed, half out-of-it – as a man who can hardly follow the mystery he's hired to solve and who melts into the riotous gallery of supporting actors (Sterling Hayden, Nina Van Pallandt, Jim Bouton, Henry Gibson, Mark Rydell, etc).
"Change is happening so fast," Deussen notes, "that individuals and systems can hardly follow".
He had many successes as a businessman, but he hardly followed a conventional route.
Yet he hardly followed the pattern of the self-promoting modern tycoon, and seldom gave interviews to the press.
For the most part, the news media hardly followed up with the kind of investigative work that makes a reporter proud.
Yet it shares its title with an Alex Callinicos book of 1991, which was hardly followed by years of leftwing advance.
The crucial distinction is not between those we like and those we don't (Solzhenitsyn hardly followed a checklist from the West Village Democrats club) but between acts of imagination and acts of violence.
