Getting 'umbrella'd' on the London Underground or London Transport generally is an occupational hazard for millions of commuters; perhaps an alternative meaning for the verb to the one you intended, but one that I think is legitimate.
With millions of people carrying umbrellas in the rush hour during inclement weather, it can often seem dangerous navigating the London Undergrpound and Overground transport systems. Most umbrellas have a metal spike at the end, and not everyone takes care not to flail their spikes where they can do anatomical damage. Especially this is the case with swaggering bankers and stockbrokers who have had a more than profitable day as they swing their brollies, in joyful abandon as they board the evening train. But I only know of one instance where someone was 'umbrella'd' to death.
In September 1978, in an old style Cold War assassination a Bulgarian defector Georgi Markov was injected with a poisoned needle (containing ricin) attached to the end of an umbrella, whilst he waited for a bus at London Bridge. Suspicion has always been on the Bulgarian Secret Police, but no one was ever charged. After a 35-year 'Statute of Limitations'passed in September 2013, the current Bulgarian government prosecutor has closed their files on the case. But Scotland Yard's files, as always, remain open! It seems certain that Markov was 'umbrella'd' deliberately with a poisoned needle.
An alternative spelling to the past tense of the verb 'to umbrella' could be 'umbrellered'
See below report: