The most common and most likely answer to this crossword clue is the 4 letter word MASK
I've seen this crossword clue in Independent
M
A
S
K
More clues leading to the result MASK
- Head of Mafia to request disguise
- Millions request protective cover
- Disguise Mike as King
- Millions beg for protective cover
- Obscure appeal by maiden
- Cover up mother’s knee at first
- After a month, seek disguise
- Bond’s boss to query disguise
- Screen opening of movie on demand
- Question mark appears at left of screen
Buddy explains!

The straight part
We know that "screen" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case screen = mask.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does MASK mean?
MASK noun- A cover, or partial cover, for the face, used for disguise or protection.
- That which disguises; a pretext or subterfuge.
- A festive entertainment of dancing or other diversions, where all wear masks; a masquerade
- A person wearing a mask.
- A dramatic performance, formerly in vogue, in which the actors wore masks and represented mythical or allegorical characters.
- A grotesque head or face, used to adorn keystones and other prominent parts, to spout water in fountains, and the like
- (fortification) In a permanent fortification, a redoubt which protects the caponiere.
- (fortification) A screen for a battery
- The lower lip of the larva of a dragonfly, modified so as to form a prehensile organ.
- (Puebloan) A ceremonial object used in Puebloan kachina cults that resembles a Euro-American mask. (The term is objected to as an appropriate translation by Puebloan peoples as it emphasizes imitation but ignores power and representational intent.)
- A pattern of bits used in bitwise operations; bitmask.
- A two-color (black and white) bitmap generated from an image, used to create transparency in the image.
- The head of a fox, shown face-on and cut off immediately behind the ears.
- To cover (the face or something else), in order to conceal the identity or protect against injury; to cover with a mask or visor.
- To disguise; to cover; to hide.
- To conceal; also, to intervene in the line of.
- To cover or keep in check.
- To take part as a masker in a masquerade
- To wear a mask; to be disguised in any way
- To cover or shield a part of a design or picture in order to prevent reproduction or to safeguard the surface from the colors used when working with an air brush or painting
- To set or unset (certain bits, or binary digits, within a value) by means of a bitmask.
- To disable (an interrupt, etc.) by setting or unsetting the associated bit.
- A mesh.
- The mesh of a net; a net; net-bag.
- Mash.
- To mash.
- To mix malt with hot water to yield wort.
- To be infused or steeped.
- To prepare tea in a teapot; alternative to brew.
- To bewilder; confuse.