The new pitch at Croke Park was laid during spring/summer 2002 in time for the Leinster hurling final but its use was limited in its first winter to minimise the damage ahead of the Special Olympics and All-Ireland Club finals, which took place on 17 March 2003.
This was the first replacement of the pitch surface in the history of the stadium. Supplied and installed by Leicester-based, Hewitt's Sportsturf, the new surface is a DD GrassMaster Desso pitch. The yarn and DD GrassMaster system, comprises of a stable, free-draining base layer topped by a layer of compost-enriched sand. During installation computer controlled machines injected a special yarn into the ground to a depth of approximately 20cm leaving 2cm above the ground.
A rye grass especially developed for Croke Park was then seeded between the artificial grass fibres. Once the natural grass has grown fully and the turf is dense, the artificial grass fibres carry out their work almost invisibly. This natural grass is hard-wearing, quick growing and has a quick recovery time, taking between only four and six weeks to grow. The close proximity of the stitching and the natural grass roots growing around the stitching is what gives the pitch its stability and is the key to the success of this type of surface. The system is employed in a number of English soccer stadia, including Anfield (Liverpool FC), Upton Park (West Ham United) and Villa Park (Aston Villa).
Source
Wikipedia