Gilbert Arenas has been hit with a restraining order after a woman told authorities the ex-NBA star has been threatening to send naked videos of her to her son ... this according to docs obtained by TMZ Sports.
The woman claims she's been in an on-and-off relationship with Gilbert since 2016 -- but recently tried to end things for good.
Gilbert allegedly took the break up badly and began harassing and threatening the woman and her 10-year-old son.
"Gilbert told me he was watching me at [my] son's school and that he had just saw him go into class," the woman wrote in docs filed in L.