You guys are on the verge of spamming.
And there are a set of averages for Batsmen(Keepers included), Bowlers, Allrounders, Bowling Allrounder and Batting Allrounders. Your performances are based on these averages. If you are in form, you'll score more or take more wickets as this is built in the sim. So it is some luck, but you stand a better chance if you are a pure bat/bowl rather than an allrounder.