First time in my life that I have witnessed that type of decision... although I did know about the Law.
Conway had left the field earlier, with the umpires' permission.
Pollard skied one and Conway took the catch. They also completed a run...
Pollard was walking off when the umpire, Marais Erasmus, called him back.
The fielder, Conway, had never informed the umpires that he had returned onto the field.
Result?
5 penalty runs, 1 single run to Pollard and the ball had to be re-bowled.
Incredible!!
Apologies for the late reply, but if anyone else had any doubt with regards to this decision, Law 2 (substitutes and runners, batsman or fielder leaving the field, batsman retiring, batsman commencing innings) is quite clear on this one:
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5.Fielder absent or leaving the field
If a fielder fails to take the field with his side at the start of the match or at any later time, or leaves the field during a session of play,
(a) the umpire shall be informed of the reason for his absence.
(b) he shall not thereafter come on to the field of play during a session of play without the consent of the umpire. See 6 below. The umpire shall give such consent as soon as is practicable.
(c) if he is absent for 15 minutes of playing time or longer, he shall not be permitted to bowl thereafter, subject to (i), (ii) or (iii) below, until he has been on the field for at least the length of playing time for which he was absent.
(i) Absence or penalty for time absent shall not be carried over into a new day’s play.
(ii) If, in the case of a follow-on or forfeiture, a side fields for two consecutive innings, this restriction shall, subject to (i) above, continue as necessary into the second innings, but shall not otherwise be carried over into a new innings.
(iii) The time lost for an unscheduled break in play shall be counted as time on the field of play for any fielder who comes on to the field at the resumption of play after the break. See Law 15.1 (An interval).
6.Player returning without permission
If a player comes on to the field of play in contravention of 5(b) above and comes into contact with the ball while it is in play,
(a) the ball shall immediately become dead and the umpire shall award 5 penalty runs to the batting side. Additionally, runs completed by the batsmen shall be scored together with the run in progress if they had already crossed at the instant of the offence. The ball shall not count as one of the over.
(b) the umpire shall inform the other umpire, the captain of the fielding side, the batsmen and, as soon as practicable, the captain of the batting side of the reason for this action.
(c) the umpires together shall report the occurrence as soon as possible after the match to the Executive of the fielding side and to any Governing Body responsible for the match, who shall take such action as is considered appropriate against the captain and the player concerned.