What splitting pattern is this?
This is the a peak from one of the vinyl protons on an allyl group. This splitting pattern is an ABX pattern from the bold hydrogen below. It is technically a triplet of doublets of doublets. 

$$\ce{R-CH2-C}\textbf{H}\ce{=CH2}$$

Check out the following simulated NMR spectrum of 3-chloro-1-propene (allyl chloride) from nmrdb.org


Now image if the coupling constants are a little different and the structure collapses into what you have.