Failure to clinch a success from a position of significant advantage either from perceived strength or the status of the competition, such as going up 3-0 in a best of 7 series only to get reverse swept and lose 4-3. While not confirmed, it may come from the idea of having it "in the bottle and failing to put the cap on it" letting it escape.
The 19-0 Patriots going into the Superbowl losing to an Average-at-best Giants team to go 19-1? One of the biggest bottle jobs in history.
To throw away a lead or a good chance of winning when you've been on the front foot. More specifically, it is when a team in a leading position loses that lead spectacularly
An example where you spend a Billion Pounds, then bottle it in finals, like @Chelsea FC
Gary Neville described Chelsea as "Blue Billion pound Bottle Jobs" as they were beaten in the Carabao Cup final by an injury-hit Liverpool, who were playing their under 13s
The definition of bottlejobs is Tottenham Hotspur because they seem to bottle (lose) every match they play or any competition they compete in. They have not won a trophy since 2008.
Jeff: "You watching any footy this weekend?"
Phil: "Yeah going to watch the bottlejobs take on Burnley"