Cricket is a battle between bat and ball; it is a battle that involves batsmen, bowlers and fielders. Although every cricket player must field and bat, there exist specialist batsmen and bowlers. Some players develop their batting and bowling skills to such a high level, that they are considered all-rounders.
In cricket, all-rounders are players who have more than one specialty (typically batting, bowling or wicket keeping). The conventional view of all-rounders is that of players who can bat as well as they can bowl. However, the concept of the all-rounder has evolved to extend to wicketkeepers or even exceptional fielders who can help to win matches purely by their prowess in the field. In modern cricket, there is a sub-classification of all-rounders into genuine all-rounders, batting all-rounders, bowling all-rounders and wicketkeeper-batsmen.
Some cricket commentators opine that an all-rounder is a player can earn a place in the team either as a specialist batsman or specialist bowler. Such a player is a genuine all-rounder. One classic criterion for a "genuine all-rounder" was that the batting average should be higher than the bowling average. However, several players in cricket bat and bowl but are merely "good enough" in either skill. They may not be able to earn a pick on a team on the strength of their batting OR bowling but by virtue of their batting AND bowling.
There are also many batsmen who can bowl and bowlers who have a decent batting average. Wasim Akram, Pakistan's lethal left-arm fast bowler, ended his Test career with a batting average of 22.64. Carl Hooper, the West Indian batting enigma, was a specialist batsman who managed to scalp over 100 Test wickets. Cricket experts considered neither of them to be all-rounders. To many, Wasim was merely a good lower-order batsman and Hooper was an occasional bowler who had a fair share of success with the ball whenever he bowled.
Some players' statistics make a stronger case for all-rounder status than Hooper's or Akram's. Cricket pundits consider these players batting or bowling all-rounders. West Indian Chris Gayle (batting all-rounder) is very effective with the ball (in ODIs and T20s anyway) but his batting is far stronger and more devastating. In 2009, Stuart Broad's batting shone brightly, making him a bowling all-rounder.
"Batting all-rounder" or "bowling all-rounder" is also a transient term for a specialist batsman or bowler who becomes increasingly better at the other specialty. New Zealand's Daniel Vettori started as a specialist bowler. He then became a bowling all-rounder and, subsequently, a genuine all-rounder when his batting average surpassed his bowling average.