Mr Gallagher took charge of two of Pompey's games last season the last of which was in their 2-1 home defeat to Aston Villa in February. Two Pompey players, Richard Hughes and Dejan Stefanovic, were cautioned during that game.
In total Dermot Gallagher took charge of 20 Premier League games last season in which he handed out a total of 50 yellow cards and 3 reds.
This season Dermot Gallagher has officiated in just two Premiership games handing out a total 6 yellow cards and 2 reds although Hammers defender Paul Konchesky's red card in the game against Newcastle was later rescinded by a FA disciplinary commission.
Mr B Baker and Mr P Kirkup will be Dermot Gallagher's assistants for the game at Fratton Park on Saturday afternoon.
For a detailed head-to-head between the two sides, click here