The initial idioms of the letter A

spear carrier	special delivery
spectator sport	a spin doctor
a spoonful of sugar helps the medicine go down	a sporting chance
spot check	a spring in (one's) step
a square meal	a square peg
square rod	a stab in the back
a stab in the dark	a stag night
a stalking horse	a standard-bearer
starting price	a steal
a stepping stone	stick in the mud
stick to beat (someone or something) with	a stick to beat with
stick up (one's) ass	a sticking point
a stick-in-the-mud	a sticky situation
a sticky wicket	a stiff upper lip
a sting in the tail	a stitch