The word 'headfirst' is correct and commonly used in written English.
It is an adverb that means with the head leading or downward towards the ground. Example: "She jumped headfirst into the pool, eager to cool off on a hot summer day."
And then, with two minutes to go, Guru-Murthy plunges headfirst into drugs, alcoholism and daddy issues.
Officers completed paperwork over Gray's arrest, placed him in leg shackles, and according to charges laid against all six officers involved in the incident, placed Gray "on his stomach, headfirst on to the floor" back into the van without a seatbelt.
My chances of succeeding were slim but, even so, I couldn't just wade into the world of agenda-setting citizen journalism headfirst.
Optimists go skydiving to experience a life-affirming surge of adrenaline, but pessimists steer clear because they know they'll plummet headfirst into a flock of geese, and then their canopy won't open, and then their plane will crash-land and explode right on top of their shattered almost-corpse.
It dragged me headfirst into the water.
Too wide to fit in the grave, the great man's coffin had to be left "stuck at an angle, headfirst, and only half way into the earth".
Her legs are covered in syphilitic sores and she is letting her baby tumble headfirst towards the gin shop as she takes a pinch of snuff.
Skeleton (headfirst) sledding, which had not been held at the 1932 or 1936 Games, was revived for the 1948 Games but discontinued thereafter until the 2002 Winter Olympics because of the risk of injury.
As the runner nears the base, he goes into a slide (usually headfirst) in order to avoid a possible tag and to stop his forward momentum at the base.
Pentecost is known for a fertility ritual performed (usually at various times from April through May) to guarantee a good yam harvest; "land divers" jump headfirst from towers up to 80 feet (24 metres) tall that are made of bush timber and vines.
St. Moritz featured the debut of skeleton sledding, a contest in which competitors, lying headfirst on sleds, raced down the 1,213-metre 1,213-metre-) long Cresta Run.
