This is the 9865th most frequent Turkish word.
ayağına
"To/at/on/in his/her/its foot."
In this sentence, 'ayağına' refers to the recipient of the action, specifying the foot as the part where the stone hit.
Ayağına taş çarptı.
A stone hit your foot.
Here, 'ayağına' implies proximity or location, indicating someone's place or rights.
Ayağına kadar geldim.
I came all the way to your footstep.
In this usage, 'ayağına' serves to indicate the subject's foot to be careful about what they do with it.