One distributing crap odds and who's opened a book? (8)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

SP (abbreviation for starting price = the odds for betting on a particular horse at the start of a race) + READER (someone who has opened a book). I assume Lette means muck-spreader = a device for spreading manure on a field. The definition could just be “one distributing”, but then I’m not sure what “crap” is doing; I wondered about odds in the dice game craps, but I’m not sure that’s relevant.