Such expressions do not seem strange to us, do they? There are many circumstances in which we come across such sayings out there, without even paying attention to the linguistic characteristics demarcated in them.
For this reason, let us take care to analyze which of them are considered correct, so that we do not make any deviations out there, do you agree?
Do we step on the grass?
This is an expression adequate to the formal standards of language, given that the verb “to step”, in the sense of putting your feet on the ground, walking, walking, can be classified as a direct transitive (step on the grass).
And stepping on the grass?
It is also correct, as the verb is also classified as indirect, governed by the preposition "in" (To tread on the grass).
But then to say stepping on the grass, as if it were indirect (which is really classified as such, but governed by another preposition), no!!!
So, know that you can say:
step on the grass
OR
To tread on the grass.
By Vânia Duarte
Graduated in Letters
Source: Brazil School - https://brasilescola.uol.com.br/gramatica/voce-pisa-na-ou-grama.htm