Why second half of Chelsea vs Nottingham Forest was delayed by several minutes.

The second half of Chelsea’s FA Cup third-round game against Nottingham Forest was delayed by five minutes after one of the assistant referees was injured late in the first period with Frank Lampard’s team leading 2-0.
Callum Hudson-Odoi and Ross Barkley both found the net for a much-changed team that saw Lampard make nine changes from the side that drew 1-1 away to Brighton and Hove Albion on New Year’s Day.
Forest, however, sent out a significantly weakened team as manager Sabri Lamouchi sought to keep key players fresh for their promotion push from the Sky Bet Championship.
Hudson-Odoi found the net early on in a game that the Blues, who had lost three straight home games, were mostly dominant.
Having been played in by a clever pass from Pedro Rodriguez, the teenager took a touch before cutting in and firing low past Forest goalkeeper Jordan Smith.
Hudson-Odoi had got the backing of Lampard and assistant Jody Morris in the past few days following a poor run of form for the teenager.
Barkley, who was making his first start since October’s Premier League win over Newcastle, scored thanks to a similar move from Hudson-Odoi as the England winger cut in from the right and shot powerfully at Smith.
On this occasion the keeper parried the attempt away but Barkley was first to the rebound and finished comfortably.
The injured official was believed to be Graham Kane, with fourth official Neil Hair stepping in for the second period when it finally restarted