This cartoon by Peter Brookes from The Times is a comment on the situation in Ukraine. A bare-chested Russian President Vladimir Putin is fishing (see photos). He's just caught a 'tiddler' (=small fish) labelled NATO with his fishing rod. The fish tells an unimpressed Putin: "Back off!"
If you tell someone to back off you want them to stop threatening, criticizing or annoying you. • Back off! There's no need to yell at me. • The press have agreed to back off and leave the couple alone. The humour comes from the fact that it's such a small, unthreatening fish telling Putin to back off — a reference to NATO's weak response to Russia's intervention in Ukraine.
NATO is an acronym for North Atlantic Treaty Organization, a group of countries including the US and several European countries, which give military help to each other.