  VFTS102 has a projected rotational velocity ($>$500\,km s$^{-1}$) and would
appear to be the fastest rotating O-type star. We show that its high rotational
velocity could be understood within the framework of the binary merger. In the
binary merger channel, the progenitor binary of VFTS102 would evolve into
contact while two components are still on the main sequence, and then merge
into a rapidly rotating single star. Employing Eggleton's stellar evolution
code, we performed binary stellar evolution calculations and mapped out the
initial parameters of the progenitor of VFTS102 in the orbital period-mass
ratio ($P-q$) plane. We found that the progenitor binary of VFTS102 with
initial mass ratio $q_0 \la 0.7$ should have an initial orbital period shorter
than $3.76-4.25$\,days, while above this mass ratio it should have an initial
orbital period shorter than $1.44-1.55$\,days. The progenitor of VFTS102 would
evolve into contact during the rapid mass transfer phase or during the
subsequent slow mass transfer phase, and might ultimately merge into a rapidly
rotating massive star. In addition, we performed Monte Carlo simulations to
investigate the binary merger channel. We estimated the fraction of binaries
that would merge into single stars and the fraction of single stars that might
be produced from the binary merger channel. It is found that about 8.7% of
binaries would evolve into contact and merge into rapidly rotating single
stars, and about 17.1% of single stars might be produced from the binary merger
channel and should have similar properties to VFTS102. This suggests that the
binary merger channel might be one of the main channels for the formation of
rapidly rotating massive stars like VFTS102.
